One of the big prevailing myths following the release of Avengers: Infinity War was that Hulk was “scared” to come out after his beating at the hands of Thanos. To be fair, the movie doesn’t do a great job of explaining what is going on there, but the Russos recently detailed it.
A couple of weeks ago the duo was on the Happy Sad Confused podcast, and they explained that Hulk isn’t scared in the movie. It actually plays back to what Thor: Ragnarok setup and what happened with Hulk and Banner in the two years leading up to that movie.
Basically, Hulk is sick of always saving puny Banner because Banner only wants the Hulk for fighting. So the two have to work out their differences, and if you’re familiar with the various different types of Hulk we’ve seen in the comics, it’s pretty easy to see where they may be headed.
We may actually see Merged/Professor Hulk in Avengers 4, and that’d be pretty awesome.