//Slight hijack, but still on broad topic//
I think Rowlings gets more attention and focus because prior to her opinions about transgenderism becoming a thing there was this vague idea that she was on the "progressive" (and I'm talking a VERY general loose social not political sense of the term) side of things and I think the Harry Potter stories connected with people in non-traditionally sexual communities.
Speculative fiction has always used "The Secret Hidden World of X" Trope as metaphor for minority or disenfranchised or other groups that feel left out. It doesn't take a psychology degree to get why "Here's a story about a person who has felt left out and different their entire life finding a secret world of other people just like them where they are both welcomed AND a hero and proves they were never broken or weird in the first place" would appeal to certain people. And she was a self made female critical and financial success with a rags to riches back story. She was tailor made for certain demographics to really, really, really like her.
So yeah I'd wager about 4-5 years back when Rowling's transgender opinions started to become part of the public discourse, it hit at a time where a statistically significant part of the really hardcore Harry Potter Fanbase, and (going on gut feeling here) a REALLY big part of the weird adult "Harry Potter and the 35 Year Olds Who Really Should Have Read Another Book By Now" fanbase was overly represented by people from non-traditional sexualities. Long story short I don't think it's too much of a leap to assume there was a LGBQT Harry Potter fandom of meaningful size.
I mean they are starting to retcon it NOW in that insufferable "No I never liked, I always knew it was rotten, I knew it before you did, in fact I knew it before everybody" way but for the longest time "Conservatives hate Harry Potter for promoting witchcraft" was the major narrative and in the modern world people do take sides in almost everything. Almost every major franchise "belongs" to either the Left or the Right and the Left "owned" Harry Potter for like 90% of its time where it was culturally relevant.
So rightfully or wrongfully the non-traditional sexual community, I think, sees a subtext of "betrayal" in Rowling, a vague, not directly spoken, not super well spelled out but still there under the surface sense of "I thought you were on our side."
If that makes sense.