I believe that it looks like there are more BL games on itch than on steam is partly because...it's fairly easier to post games here than on steam...like posting on steam is more formal, and itch may be more casual, so there are quite a few short BL games here, which you can't see on steam. Idk, just a feeling.
And as for your edit...I think that's true xD as I am Chinese too, I often notice games made in or featuring Chinese elements. I don't know if this is because I only check out the Gay tag or not, but the popular ones would mostly be fangames of Chinese works (like Genshin or MDZS). Original BL games that are really popular and is purely about a Chinese topic, well...I haven't found one yet. The concepts are pretty hard for foreigners to understand I guess :P
A possible way to solve that is to simplify the terms, and add original ideas into it, for example, Genshin Impact again, or Qiu in Our Life Now & Forever. But then again, you can't say these games are completely 'Chinese' as well.
When I make games myself (currently just ideas), I would like to put some Chinese characters/elements in it, but that's all. Introducing traditions and cultures is too hard a task for some regular student like me xD
Ummmmmm and why didn't I just use Chinese in the first place???
总之加油,我们都有光明的未来,以及难道写论文一般的长感想是中国人特有才艺吗xDDD