Gays are a minority, Inside of that minority how much are into stuff like cartoons, anime and videogames?
Now, Inside of that already little minority, How much actually jack-off with 2D stuff instead of the usual hook-ups?
hetero hentai its a gold mine, most artists would never waste resources and time to satisface a tiny market in comparison to a ocean of money.
In the case of japaneses, in the past decades with mostly OVAs they could be more experimental, thats its the reason of why styles and plots were more "diverse", that time last until 2010s when things starting to be more "standardized", so, they never take the risk to satisface niche fetishes.
That can apply to ASMR, vtubers ans cosplay porn too, gays are just too "normie" for that.