Multiple theories about that, as I've seen it unfold exactly like you have. I've also frequented that sort of people but I'm someon with ten thousands interests and no big huge all consumming passion, so I dab a little bit in everything and mostly do nothing.

My theories :

• Time efficiency. The more you focus on one very special subject the less time you have to stray off it. So the more precise your hobby the less you're wasting time puttering about. Might make sense when your job is very demanding. Turns into obsession. Probably the least likely in most cases, though. But also makes sense when you have one buget into which you can pour money in.

• Credibility and misogyny. Women's hobbies have always been seen as frivolous. Being a litteral expert in something might be a response to men mocking you, not trusting you or not believing in you. Usually ends up being unsufferable because so highly opinionated by defense. This encourages conformity because anybody who strays from the accepted praxis is seen as weakening the credibility of the whole group. When it comes to old timey things it obviously encourages a desuet femininity.

Finally, just trends. Corsets made a huge comeback ten years ago, then it was Rockabilly, extremely femining BJDs and dolls in general, then there was a huge make up industry boom. We're currently highly encouraged to be extremely feminine and that can push passions into the kind of things you've seen. Also there's more men that feel comfortable dabbing in fantasy clothing too, and with that comes to pressure to fall neatly into gender roles all over again.

Hope I've not missed your point entirely!