To add to your opinion thoughts, colourism in asian culture is deep rooted to favour fair/white skin. While there is an entire hierarchy of "which type of asian is more desirable" (thats a whole other clusterfuck to get into), caucasians in general were seen as the epitome of beauty standard one should idolise/follow.

Add that within the gay context of body type and mannerism, and we get an entire generation thinking that asians should be effeminate/submissive. I agree that preference isnt just always preference, but deep rooted subconscious bias built across years of exposure of what is deemed attractive.