The reasons generally start out personal and become generalized as a political “position”, which really consumes your life after a while.

Rowling has said that she had a queer “phase” and that if she were going through that nowadays, she would likely have ended up considering herself trans (incorrectly, by her assertion). That reads to me as some internalized bigotry that she never worked through. Musk has a daughter who’s a trans woman and disowned him for being a piece of shit. He started posting about “pronouns” soon after. And Zuckerberg seems to have seen the way the winds are blowing with the current administration and jumped on the anti-trans bandwagon because he’s a lizard man with no soul (metaphorically, not in the David Icke antisemitic way). These are all guesses, but not based on nothing.

It ends up being socially unacceptable to say, “trans people remind me of my estranged daughter so I don’t like them,” and rightly so. So you have to retreat and bury the context, taking it up as a matter of principle. And your mind can backfill the justification over and over again, further cementing the ideas as people start to ask you to talk about trans people over and over again. After all, you’re a public figure who doesn’t like trans people. That’s a hot topic. People on Twitter want to talk about it. Reporters want to talk about it. So it snowballs from there. Transphobia can absolutely take over the life of a public figure.

Philosophy Tube has an excellent video on something called phantasms and how people get stuck in irrational worldviews. Would recommend.