Now that you mention it, I noticed something... it looks to me that there a certain people or companies that specialize in doing BL mainly, and that these projects are not considered as "a main production" but more like an "independent project".
In my country, if people do an LGBTQ+ themed movie or series it would be an unusual theme, and the people involved would be quite well known because the theme would be considered edgy and a project that could expand their experience and acting skills... the names would be big in productions team as well and so on. But if there would be some kind of BL company promoting LGBTQ+ (a company that is not mainstream, a company that wants to represent BLs), it would be an "indie" company, they would cast more up and coming actors, unknown people, and the budget would be small, the resources would be limited.
I think it's the same with BL in Asia the industry is not mainstream, the audience is not that diverse and big (the target is mainly girls), the budget is not that big to afford that big names and there is a stereotype in these type of projects... We also know that sometimes they crowdfund or they put in their own personal money.
Also, there is a thing that I noticed in Taiwan for example, even if they are open-minded (could be people are only minding their own business) bay people are not coming out that much (I mean famous people), could be they are afraid that they will lose the diverse audience or be typecasted, and the ones that were outed are big names that did not do BL projects, also we have to consider their positions in the small circle of family and friends, young people were accepting but some did say parents did not.
So it could be that not all actors that are big are thinking to go to the BL industry because generally, I saw some big names doing LGBTQ+ projects but the movies were big projects.