Because ppl dont get the simple fact that:In that case I don't understand OP's question. Being sexually aroused by a cock penetrating a man's asshole is obviously gay.
Gay: only attracted to same sex
Bi: attracted to both sexes
Straight: Only attracted to opposite sex
Neither is about anal sex or cock.
You dont it get either, and thats cool and all. So this topic is made by someone like you.