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