Why all the mucking about with space portals in The Avengers?

Question

In The Avengers (2012), Loki is sent to earth via a one-time bridge to the tesseract

(a powerful artifact recovered from Norway that we later discover contains an infinity stone).

His mission, presumably, is to recover the tesseract for Thanos, and his reward for doing so will be right to rule Earth. To aid him in his quest, he is given

another infinity stone,

and command of an army that will conquer earth for him once he uses the tesseract to open a second, more permanent bridge through space to allow them in.

Why? Why all this monkeying about with space bridges? We know from Avengers 3: Infinity War that

Thanos has ships than can travel vast distances in almost no time,

and we've seen similar speed from the ships in the second Guardians of the Galaxy movie. Why give an infinity stone to a god of mischief, and run the risk of his stealing or losing it (as indeed he did for time), when Thanos could have just flown over and grabbed the thing, or had his minions do so?

Answer 1

Thanos is working behind the scenes to try and get hold of the Stones. He's not the only powerful force in the universe, and once it becomes known he's seeking the Stones, those who have them will take extra steps to protect them quickly, and so he starts out trying to retrieve them without being directly involved.

In Guardians of the Galaxy, he tried to have Ronan get him the Power Stone, and as you say, in Avengers, he gave Loki what we later discover is the Mind Stone to retrieve for him the Tesseract (Space Stone). None of these plans worked out quite the way he had intended - Hence the "Fine, I'll do it myself" end credit scene of Age of Ultron.

He may also have been waiting for specific characters to die. There's a popular theory that had the like of Odin and The Ancient One still been around, then Thanos would have found it much harder to complete his collection.