I'm pulling this out of my ass, no pun intended, but I've always imagined it as homephobes distancing themselves from anything gay, especially being gay and liking gay stuff.
Like as in they would never go to a gay bar with their gay friend even though they platonically like the friend, enjoying dancing and so on. If gay stuff is on TV they have to affirm the mantra "I'm not gay so I don't like stuff" so they use slurs to reaffirm their stance.
There's also the thing where people view manly and gay as opposite. They identify as manly so they have to not like gay stuff.
Bottom line, I think they're insecure about their masculinity, afraid of actually becoming gay or both.