dude i dunno. i guess because it’s more difficult for people to get off to two 50-year-old asian men than it is for them to get off to a het ship w/ a white girl for them to project onto
also it’s hard for fandom to be interested in a m/m ship unless both members are young or white. and even then unless they’re white it’s hard for fandom to sustain interest (see: finnpoe). it’s like the layers of m/m shipping