The idea behind the Dirty Sanchez, and its associated sexual acts, appears not to have come from the gay community, but from the straights imagining what gay people do, in the manner of preadolescent school kids telling each other stories like the "Lesbian Lobster Lover". The mere idea of taking your peepee and putting it ... where? in a yucky girl is so odd and scary that they make up stories about horny teen girls dying of impalement on a broomstick, or lesbians making it with lobsters, who shit shrimp eggs inside them, or...
The fact that gay men put their peepees into each other, where it's dirty and all, just doubles and triples the disgust/fascination. (That they do sometimes do other things that "vanilla" straight people find completely odd is another factor.) Anyway,I doubt if very many people have either done it or find it all that great.