ScreenRant recently talked about how co-writer of Avengers Endgame Stephen McFeely finally answered the question of why we never got to see that Hulk vs Thanos rematch many of us looked forward to. As one of the people that was initially annoyed by this I have to admit, it makes a lot of sense. The general idea is simple. After the snap, he learned to be more one with the Hulk and became Smart Hulk as the MCU calls him. Because of this, it was no longer a driving force for him to fight Thanos or anyone else.
That is it, that is why we never got our rematch. Because Smart Hulk had no desire to fight him again. Now while this does make sense, I will admit I still would have enjoyed seeing this. Going forward tho smart hulk can be quite fun to watch. Best wishes and may the gaming gods bring you glory.