As far as I can see it's because they read articles on him by other people, or small videos/quotes, and don't really engage with much of what he says.
I always find it really interesting too that some of the things people get twisted about are pretty standard things he talks about from within his discipline and not all that controversial. Although I guess that is maybe not unusual, I've known a few people to get really hung up on things that are considered standard basic uncontroversial facts in my own discipline too. There seem to be some things that the general public think are live controversies which really aren't.
Some of the articles about him, for example from the NYT have been inaccurate enough that I would say they were irresponsible journalism - I remember a few claiming he advocated forced marriages based very much on their own misunderstanding, and really they should have been withdrawn. But weren't.
If you ever hear him talking about women in the workplace etc it's pretty clear that he supports women doing pretty much whatever they want, being supported to do so, and against abuse, by the law, and advocating for themselves. He does think that women have different issues in the workplace then men, but so do a heck of a lot of women.