I'm afraid it's not just Wikipedia. It's pretty much everywhere on the Web. Cf. "Gamergate" which, regardless of what you believe about the origins, has turned into an on-line orgy of misogynistic bullying.
I see two reasons for it:
1. Anarchy. To actually stop Wikipedia editors from bullying women, the overwhelming majority of Wikipedia editors and the people who maintain the site would have to get together and agree on rules that would stop bullying. But not having rules is what attracted a lot of them there in the first place.
2. A misogynistic culture. We (in the USA, at least) live in a culture that is full of misogyny, racism, transphobia, etc. So there are going to be a lot of misogynistic people around (not to mention racist people, etc.), in Wikipedia just like everywhere else, and even the ones who aren't are likely to see misogyny, etc., as normal. The bullies at Wikipedia can rely on their fellow (mostly male) editors and admins to not take misogynistic bullying seriously, and if the bullies have managed to become buddies with their fellow editors, etc., they can even count on their support for the bullying. Kind of, "I believe him because he's cool to go out for drinks with." (Same for racism, transphobia, etc.)
Note that "outing" (or doxxing) also only works because of society's misogyny, etc. "Outing" someone as trans is only of use to a bully because they can count on society at large treating trans people badly.
