This is one of the lesser bad-professor archetypes (the personal errand slaver) that surprisingly exists in real life. And much worse archetypes also exist and persist.
Like many professors behaving badly, you'd think they'd get exposed and corrected. But grad students and postdocs (in a position to know what's going on) don't want to throw away their careers. They need the recommendations, they need to not be seen as damaged goods from a bad advisor, and they need to not have sketchy university administrators getting rid of the messenger. And if admin assistants notice, they probably need the job, especially if their kid is getting a tuition deal because the parent works at the university. To a bad professor, the environment is like a heartless business, only less accountable.
When a friend was telling me about this brand new grad student, who'd be working with professor X, I said "Oh, no..." and that X was bad to students (which I knew from one of their students). Friend, who was from a prominent academic lineage, immediately responded crossly, that I shouldn't say such things, hurting people's reputations. Soon after, friend came back and apologized, that I had been right, and the student realized their terrible career move, getting that advisor. Friend later connected some prospective student to me, to warn them about a different bad (worse) professor in the whisper network.
But universities have terrible institutional memories, with students always leaving. So a bad professor tends to persist.
Though, occasionally, you'll hear of a bad professor from the whisper network leaving their job, without explanation. So presumably a wronged student or staff finally sued.