I think they started going in one direction for Thor and that played all the way to Age of Ultron, but by the time Ragnarok came out, we had a different, more comedic Thor, and they decided to stick with that version of him.
That was a bit much for me because not only was Pepper SO against Tony putting himself in harm's way to save the world in Infinity War but then she goes and does the same thing in Endgame despite the fact that they now have a child.
I think they want to emphasize the fact that Peter is still new at this and in over his head. Quipping would make him seem too confident.
When I found out about him being in Captain Marvel, I was almost certain that would mean he'd be in Endgame too. Kind of a tease, I'd love to have seen him make an appearance here.