Simple. Because like so many things ''Mozart'' ~ such a plot SELLS ... That film is PURE FICTION ... It's the OTHER WAY AROUND: Mozart was not yet so successful, he was still making his name known, at the time of his death - he was still in the process of educating himself (van Swieten & AMZ anecdotes and reviews), his abilities were growing, he was fortifying his position in Vienna - but Salieri was already firmly established: tremendously famous, fairly well provided for, well positioned at court (as royal Kapellmeister he held his job until the day he was no longer able to perform it or died) and was commissioned by major opera houses throughout Europe: Salieri was threatened by Mozart as an elephant is threatened by a blade of grass (like the 7th February 1786 challenge confirms) - meaning: not threatened at all, his references or witnessed spoken words on the ''subject: Mozart'' ~ are immensely scarce - he simply didn't bother and wasn't bothered - but instead it is, rather and as with so many things ''Mozart'' in this excellently mythologised canon ~ the OTHER WAY AROUND: Mozart had to work his arse hard and compete with fame and abilities of Salieri - and other, best selling composers - and Mozart's bitter personal attitude attests to this fact ...
Read Mozart's LETTERS in original German (translations are wrong, full of mistakes and censorship) - entire family spits ACID towards Salieri (and almost every other successful, clever and skilful composer they were envious of or felt threatened by) - while there is no similar wording from Salieri - or others - about Mozart: Salieri, who was original, inventive, revolutionary, melodic - and difficult to perform operatic composer ~ had absolutely no reason to dislike Mozart ~ other than the fact that Mozart, like from many others, borrowed ideas and themes (and works) heavily from him. Which was, mind you, a well known fact at the time (Albrechtsberger anecdote: ''I don't believe what they say!'' - what were they saying about Mozart at the time?!) - which, amongst others, played a major part in Mozart not being able to find a job - pretty much nobody wanted him.
This would be a good opportunity for you to explore operatic masters of 18th century, especially Viennese: Y Soler, Sarti, Paisiello, Anfossi, Cherubini, Spontini, Mysliveček - R. Kreutzer wrote 29 operas and ended up as principle conductor and later director of Paris opera (here are his full credentials: Violoniste et compositeur - Membre de la chapelle royale (1783-1792) - Membre du Conservatoire (1795) - Professeur de violon au Conservatoire de musique - Maître de la chapelle du roi (1815) - Directeur de l'orchestre royal (1815-1827) - Second chef d'orchestre (1816-1824), puis directeur de l'Opéra et de la musique (1824-1826)) - yet you'll find him ''barely worth mentioning'' and that only as meagre and ungrateful a footnote to Beethoven's ''Kreutzer sonata'' - you'll hear that most composers have their own special branch of geniality - which will on many happy occasions leave you breathless and in awe. You will also learn where Mozart ''got it all from'' ... Meaning: out of about 8.500 composers just in 18th century period - Mozart was far from ''the best''. Such notion - is legacy of Romanticism - out of which the ''Amadeus'' story derives from. Why Mozart has to be kept as the very peek of the non-existing musical pyramid and hierarchy - I don't know - some say it has to do with early nationalism and pan-German ideology and others say it's masonic Lichnowsky conspiracy, then we have a roughly estimated 5 billion (!!!) € income Salzburg pockets each year through tourism, etc - but personally, it is impossible for me to acknowledge any such a structure, especially after hearing works of hundreds of masters of music, Salieri amongst them.
One important lesson we must keep before our eyes: in Mozartian canon - most things are not what they seem and are in fact - THE OTHER WAY AROUND ... Anton Eberl, it was mentioned in his obituary, was famous for composing ''out of his head'' - Mozart needed the piano (he says so in his own letter) and Eberl's works were in lifetime of both attributed and sold as Mozart's, he was the one being jealous of Salieri's position and achievements - not Salieri of Mozart's (Salieri already had a considerable and formidable mileage to his credit - Mozart scarcely any), Mozart didn't have a perfect memory (Allegri: Miserere, copies of which were circling around since before Mozart wrote it down, as the chief gatherer of music and instruments for Archbishop - Leopold was also in contact with two out of three of possessors of Vatican copies: the H. Roman Empire's court of Leopold I in Vienna and PADRE MARTINI whom Mozart VISITED before attending 1770 Holy Week in Vatican ... Other copies were made by others and loooong before that.) Mozart did not compose with ease (revisions of two years of writing the Haydn quartets), he was not originator of many of his works (publishers were forging his name so that the compositions sold - he also made copies of works of others for his library - which ended up attributed to him, etc.) - or ideas he used (frankly, you can trace these wherever, even in Salieri's ''Te Deum'' of 1790 - first and only ''Mozart's'' 8 bars of Lacrimosa), he was not all love and roses (like L'Opera Rock would have you believe) but envy, mean tongue and mistrust, he was not born with knowledge nor did he ever fully grew as a composer - but was learning to the last (Marianne: ''My brother liked his older compositions less and less the more he ADVANCED in composition'' - meaning not all of his music is of high or the best or perfectly accomplished or of whichever ''quality'' (music can not be judged through or described in such terms anyway) - he was working to IMPROVE himself constantly, he was learning), he was not so much a revolutionary than the follower of what others did and invented before him - he then skilfully used their knowledge (like he did Vogler's) - and he did not write ''Requiem for himself'' as later about 1820' anecdote by Aloysia (?) would have it - Michael Haydn said that at his own death bed (1806) whilst composing his unfinished Req No. 2 and Joseph Haydn was the one who played that impossible note with is nose on the keyboard ~ A LOT of what was done and achieved by other composers - became a conglomerate of what Mozart supposedly is - but it's all a fabrication. Only now are we free to get to know real Mozart, without perfect romantic prejudice, warts and all: he was beautifully human.
Mozart has been a constant source of manipulation and lies since he was 4 years old, first by his father, then by himself, then by his widow and his worshippers. Romantic stories Hollywood used to swear by needed a Brilliant Hero who's been wronged - but prevails at the end: all wrongs are made right, most movies (and world literature) are made like that, it's a magic formula. But it's also pure fiction. Lives are not black & white, hey, in his lifetime even old Salieri was not bulletproof material, he had his flunks, had to be diplomatic in order to make the most for his works as even the mighty champion of ''Italian camp'', count Orsini-Rosenberg, plotted against him ... Not to mention the dreadful cabals each composer was prone to experiencing at least once ... And just to point out how wrong ''Amadeus'' movie is: Salieri wasn't ''addicted'' to chocolate - but to SUGAR ... :D
At the very least we, from Mozart's letter, know that Salieri openly recognised and supported Mozart's ''Magic Flute'' - meaning he praised Mozart's abilities and music - openly and in view of the public. And it was not a hired choir of professionals who sang Salieri's Requiem - but his pupils and his FRIENDS; the mass of people who sang their farewells to their master, teacher and a friend that day - speaks the most of Salieri's true character. He was loved and respected - for a good reason.
Sources: Il Caso Salieri (Della Croce, Blanchetti), Maligned Master (Braunbehrens), Fatti e Documenti (Angermüller), Mozart in Vienna (Braunbehrens), Mozart's Women (Glover), Allgemeine Musikalische Zeitung (all issues make an exciting educational read!), Mozart - a Life (Solomon), Four lives in social context (Halliwell), Beethoven - construction of Genius (DeNora), German music criticism in the late 18th century (Morrow), Ueber das Leben und die Werke des Anton Salieri (Mosel) and so on ... Plus music of others, of course, starting with Michael Haydn's Requiem of 1771 (if you wish to understand Mozart's music - you should seriously dive into entire recorded Michael Haydn's opus (about 150? out of 837 works on CDs) ~ and then re-listen Mozart with fresh ears - you'll find many tight stylistic similarities (which young Mozart picked up from older Haydn)) and Handel's Messiah. And then just roll everybody else whose music you ever heard mentioned in context of Mozart = an ear opener.