They were gatekeeping against men, but the mockery of AGP was no less vitriolic . The problem was that men would go in there and say 'As a man' or 'Man here, I think...', making it really obvious that they were men. That would attract the mods' attention and then they would go through your post history and ban you if they found anything non-kosher. If you just didn't mention your sex and kept it vague, they'd assume you were female and leave you alone. They couldn't actually get rid of all men, and men who wanted to participate had to learn to be subtle.
But of course Redditors are allergic to subtelty and can't help but powerlevel, because that site is designed for exhibitionism. It's not an exchange of ideas, it's a competition for upvotes and awards to see who can have the most tragic backstory. That's why evertyone fell for that 14 year old cancer trick, that's why pictures of ugly pets or disabled people always make it to the front page with hundreds of awards. The people giving shiny avatars that cost real money are like those guys who sit in the front row at the strip club cramming 20s into a stripper's asscrack: they want attention just as much as the person making a performamce of themselves in the OP.
In the Gender Critical network of subs there was no less exhibitionism (men are trash and my daddy's abusive because he told me to shut the fuck up once

), but they had an influx of trannies posting their sobstories in the comments or men coming in and desperately trying to show that they were 'on side', and the dykes got pissed off by it. Men were thinking that if they showed that they were supportive and also male, the radfems would say 'oh he's one of the good ones'. This is what happened in Libfem spaces, resulting in mods and admins of apparently feminist communities being male trannies or other men. Itsafetish was always radfem, and when rightwing subs like consumeproduct started noticing 'based fems' I believe that the mods became anxious about right wing men wandering in and causing issues, so they tightened the rules. You could discuss AGP on right wing male-centred subs, but the discussion was always shitty because those subs were full of the same exhibitionist retards as the rest of the site, and the mods let them do whatever because 'muh free speech', resulting in an Frat-house environment full of masculine posturing and shit-flinging. It's no suprise that people preferred the matronly no-nonsense moderating of the female subs. In short- itsafetish, trollGC and the others excluded men because men were consistently shitty.
I think that having an all female sub would have been fine to be honest, because
how would you enforce it? Aside from going full blackpeopletwitter and having people dox themselves from a flair, all the mods could do was pick out the comments that looked 'male' and follow up on them. Perhaps it would have encouraged people not to sperg out their personal stories all over a public forum full of dox and cp happy loons. At the very least, it cut out on the dick-stroking 'As a man I agree that men are trash' comments that were cropping up.
In short, the trick to not getting banned from 'no boys allowed' subs is to just not be a man. In fact, don't be a woman either. De-gender your language and quit sperging about your personal life. Sex is meaningless online, you don't have to be male or female.