I think there's a lot of moving parts to the reaction.

The long wait for Winds has made it that a lot of people have their own headcanons now. And I think we'll see more of this if and when Winds is finally published. There are a lot of theories that have reached canon status in the fandom, like the Blackfyre theory that is just taken for granted. Our headcanons don't matter. We're not writing the books and we have no influence over what George does or doesn't write. We all have our own theories, but they just theories.

I think another thing is that the fandom seems to despise Rhaegar. Love him or hate him, GRRM has made him a central character where the prophecy is concerned. He is probably the most important dead character connected to this. If I think that a character is trash, then I don't want them to be right and I don't want to give them their due. It's just human nature. Ditto the hatred of the Targaryens.

I think it's possible that there are readers who don't like the magic aspect of the books. I know there are those who don't like that the Targaryens and Starks have some kind of magical blood. But they've been at the center of this from the beginning. Knowledge of the prophecy and what's coming only reinforces the magic.

There's probably more.