As others have mentioned, they think that "representation" is important for one reason or another.
The problem is that original characters made with social justice in mind don't sell. That assume that popular characters are popular because they are popular characters. Thus is they make character X black, a woman, gay, etc. then that character will be popular and "the message" will spread.
When this backfires, there's always some excuse. An alt-right hate campaign, lack of advertising, lack of publisher support, or any other excuse. Or as
@Krokodil Overdose said-
Another part of it seems to be that they want to destroy things that are liked by the people they disagree with.
And some of them are just so dumb that they don't understand what people like or why.