I've heard the argument before that it's tied up in misogyny, homophobic men are, consciously or otherwise, thinking basically "I'm afraid gay men will treat me the way I treat women"

Hence all the anti-gay jokes like "backs against the wall lads" (note how the straight men are often imagining themselves as the bottom) - implication being, "I don't respect consent therefore what if the gay man who's more of a threat to me physically doesn't either"

No idea how accurate this is but it certainly rings true for some behaviours