Oh finally a thread I can yap in.
As someone who is Bisexual and currently dating a femboy (with both of us into Bleached), I think the answer lies in who is who on this link's hierarchy but also as well the natural evolution of the gay community's tastes.
For starters on some context. A Femboy, or Twink as they used to be called, were generally the bottoms in a relationship. That's not to say there was never a Top twink/femboy but generally speaking they bottomed. Though rare at the time there has been an uptick in their numbers. Which I believe is in conjunction with gay acceptance rising too. When you add this specific kink into the mix it comes with the expectation that non white men are submissive, full stop. So non white men with Bisexual or Gay leanings that were drawn to Bleached were almost always going to be submissive. Generally speaking the submissive male tends to adopt more feminine traits which can easily snowball into being a femboy.
For white femboys the waters get muddled. You have the more submissive white guys who drifted towards being femboys because they preferred to bottom in a relationship. Though that does put it at odds with the idea of Bleached being about White Men & Women being Dominant. To be honest there Bleached as a community never really worked through that part. So we just have white femboys who are submissive but still like the idea of the white worship that Bleached provides.
There is definitely an argument to be made that being terminally online with a massive porn addiction, ironic considering where we are, has created many fake femboys that are just living a fantasy.
Finally to address your question:
1. The forums are very small schism of the Bleached community. 99% of people in Bleached only go to the front page or search up specific tags. You have to be a little crazy to come here. So a lot of what you see people talk about on here is a small minority.
2. As for why I like femboys? I have always been attracted to the slim runner/track star body physique for both sexes. So when my first gay encounter was with a femboy that was a marathon runner by day, I was hooked since then.