Then you haven't been paying attention.

JKR is not just some writer who happens to be transphobic. There are plenty of distasteful writers I still enjoy - the difference is they didn't turn their bigotries into a project.

She has made transphobia into her whole life. It is her primary political goal. It is what she spends her money and time on.

Elon Musk (who disowned his own daughter after she transitioned) complained that JKR's Twitter contributions were too obsessed with trans people.