Not really unless you want to see homophobia it would only be pure logic that goes with the story.
Let me explain
Most of those story start with "in that BL they become attract to each other once something happen" so before that "event" there is no "sexual attraction" nor "identity"
For example in that novel Marquis guy is more involved when Monster guy try to escape and this is the first "starting point" to them being a couple
Now with the transmigration things. Girl get involved between the two of them. So no starting point. They didn t turn straight, they didn t have "sexual preferences at first until the starting point" Marquis and Monster guy didn t devellop any feeling to each other.
If you goes by that logic then BL are "heterophobic" because a loooaadd of them are turning "straight guy' into "homosexual" without adressing it but just saying "I am attracted to him now"
It's just a way to create a story line, now if you have preferences for BL then don't read this type of story line. If I was to be angry and saying it is unfair every time a girl was dump in a BL/Yaoi I wouldn t go read them!
every manhwa that is "transmigrated into a bl novel then the characters whom got turned straight sexualities are never adressed again" feels strangely homophobic lol