I hope to god this doesn't happen, it's a trope I dislike. I'm not sure if that's a normal talking point in Japan but being into dudes isn't something you can just toggle off and I hope mangakas stop using it.
It's not a trope. It's something that is happens in
many cultures. I don't know if you come from a place that being gay is accepted but its wildly not. Japan is still a conservative country that doesn't even have gay marriage legal. If you ever live or come from a conservative background then you would understand it. Yeah, its fiction but the whole point of the manga is writing what they know and what their society taught them.
This is something I HATE when other people say "why not ___" "I dislike because xyz" on non-anglo countries. I'm from the USA yet I know how other cultures are in how they treat the LGBT. We are not handled the best right now but its a lot better than other places. I highly suggest talking or do research in how thee LGBT in treated in Japan and non-anglo countries. Do I dislike it as a conflict in plots? Yes but the same time I understand why. In Japan, being gay is still seen as a "foreigner thing" + the classic "we don't mind you being gay but we would rather not see it" which is still common in the USA.
I get why you hate it but a lot of countries are not at the same level of acceptance as the anglo countries