So, forgive me since I was not a huge comic book guy growing up but, is it not unreasonable to think that Thanos is actually stronger than Hulk? Or at least this movie version of Hulk? I mean he did beat the you-know-what out of him rather easily. Or is that basically blasphemy?
As a fan of the movies but not someone who has in-depth knowledge of the comics, I did assume during the movie that Hulk got destroyed by Thanos and just didn't want to come out and play anymore. Whether it was fear or pride I wasn't sure, but I thought that beat down was what was keeping him at bay, not some frustration with Banner and his role.
I know thats not what the above link says, that was just the read I got as a lay-person watching...