I'd quibble with the "trying to add".
However, I think I have some parts of the answers to your question. As long as women, or queer people, or black, or other minority groups were confined to the margins as teammates, tokens, or fringe titles, then they were no threat. They were an alibi. "Some of my friends are black."
But once the former marginalised group becomes too successful, there
will be a backlash. The Sad Puppies, Gamergate, and similar movements are violent examples, both because of former marginalised groups demanding space both in general and doing so successfully in the creative areas. Samuel R Delany wrote a really great article on it in his "
Racism and Science Fiction".
Or Youtuber fandom musings in her movie essay "Attack on Captain Marvel: A casual look at the backlash against recent female lead superheroes" looking at similar mechanisms against women.