why can’t yaoi boys ever have non weird male mentors

I love this story but i hate how in almost all talks the man who like raised them since they were young or was there for them always has feelings for the uke. like why can’t they be like a father or big brother figure who wants the best for them and wants to protect them. why do they fall in love with the uke the second they reach adulthood i get its yaoi but cant we have a good non related sibling or father dynamic