I don't really understand where from they took those parts. Usually trailers contain main scenes from the film to convince fans to go to the cinema. But Infinity War trailer contains scenes, that film didn't contain. They fight in the woods, Bruce turns into the real Hulk and Wakanda is left a long way behind.
Why did they include parts that were not in the film?
They wanted to keep the surprises intact for audiences. Also notice that in trailer, Thanos is shown having 2 stones when on Titan, but at that time he had 4 ! This was done to remove spoilers.
Russo brothers said that
“We use all the material that we have at our disposal to create a trailer. We look at the trailer as a very different experience than the movie, and I think audiences are so predictive now that you have to be very smart about how you craft a trailer because an audience can watch a trailer and basically tell you what’s gonna happen in the film. We consume too much content. So at our disposal are lots of different shots that aren’t in the movie that we can manipulate through CG to tell a story that we want to tell specifically for the purpose of the trailer and not for the film.”
I agree that nowadays people judge the entire story based on trailers, even for Avengers:Infinity War, some fans assumed all will go well, and here is where they were wrong !!
Please find the source of my quote and other mismatch scenes here
The trailers are usually completed for screening well ahead of the film, so not only can the shots change drastically during final editing but those used in the trailer are often chosen for their impact while not spoiling any specific story points from the film.
The shot you have alluded to was created as a 'deliberate misdirect' by directors Anthony and Joe Russo, reported Collider when discussing the brothers appearance on Josh Horowitz’s Happy Sad Confused podcast.
The duo confirmed... that when putting together the film’s trailers, they wanted to keep the surprises intact for audiences. Joe Russo explained that they used footage captured for entirely different scenes to stitch together that hero shot in particular: “We use all the material that we have at our disposal to create a trailer. We look at the trailer as a very different experience than the movie, and I think audiences are so predictive now that you have to be very smart about how you craft a trailer because an audience can watch a trailer and basically tell you what’s gonna happen in the film. We consume too much content. So at our disposal are lots of different shots that aren’t in the movie that we can manipulate through CG to tell a story that we want to tell specifically for the purpose of the trailer and not for the film.”
Anthony Russo confirmed this hero shot was never in the film to begin with: “That shot that you’re referencing was never in the movie in the version that you saw. It was never even created for the movie in that version. It was literally created in that version for the trailer.”
