When I first made the site, my wife asked me if I had videos of women doing the exercises. So I added them. Simple as that.

It's probably a losing battle.

I shared the same thought as the OP and went clicking around to see if there were differences in the suggested exercises based on sex. If you intermix the videos you're going to have people wondering if the exercises demonstrated by a specific sex are recommended for that sex.

To put things in perspective, I think the fact that the muscle models had hair and the male was pigeon toed from behind bothered me more than anything else.

My guess is to be inclusive to both genders. Showing only a guy's body would be implicitly biased.

but wouldn't the be better to have videos of men and women for the same exercise, without separating the same muscle/exercise for men/women?

Yea, it's a bit odd. There are only a handful of gender-specific exercises in the directory[0], but that seems to be down to having a video for it.

[0]https://musclewiki.com/Directory

Yeah, I actually have a big backlog of videos to edit.