Because it involves co-opting an established IP and changing something to suit the ideology of people who don't like or respect the IP to begin with. It's betraying the people who are the fans of the IP for a shallow politicized reason. This usually results in a poorly written story and characters which makes people dislike this stuff more.
If someone wants characters with certain traits, they can create their own original IP with a story that makes sense with those characters. Just leave other people's shit alone and everything is hunky dory.
New characters are constantly introduced in shows/series, and new revelations of established characters are also commonplace. If nothing is different at all then there is not even a point of having a sequel as it'd be the exact same thing.
That's not how it works in most of these instances. They typically just change the characters or remove them to be replaced by whatever gender, race or sexuality they had in mind.
I'm all for new characters but they have to make sense within the story and be meaningful.