Good question. Part of it's inevitable and not necessarily intentional: a series that consists of good looking men killing each other with phallic objects is going to have a bit of a homoerotic vibe to it no matter how many women the author has the characters fuck. And when you then have to make the characters mostly apathetic towards the various gorgeous women in the series due to the series being targeted at kids, this is amplified quite a bit.
But then there's stuff like the OP's image which basically screams WRITE YAOI FICS ABOUT THIS PAIRING. (Which is especially disturbing in the case of those two, because they happen to be father and son.) No explanation for that one.