Sometimes they want to try a different take on a character to switch things up or keep things interesting. Things can get tired in a hurry if they are always the same. I for one think the more comedic tone of the last couple movies with Thor has been really good for Thor. Thor Ragnarok is my favorite of all of them. I feel bad for people that think Thor is their favorite hero and theres no way he would actually let himself get like that...its the same thing as people who hated the last jedi because what it did to luke skywalker...it hurts the overall legacy to see a character look and act pathetic especially when that person is supposed to be a hero. But for the purposes of making movies--i think its wise for them to occasionally switch things up with characters to keep things fresh. And what they've done with thor i think allows for more movies with thor in them. Whereas i think they have run their course with iron man and captain america and hulk. Although i can see them coming up with someone that takes iron mans place- discovers his suit or something. Its obvious with spiderverse that anyone can be spiderman. I think that may be a direction they go is having a black captain america, or a new iron man or iron woman, or a new hulk thats not bruce banner etc