Patriarchy says that things that are coded as male are better and more valuable than things that are coded as female. Women have sex with men, ergo if you have sex with a man you are like a woman and therefore less than. It’s the true root of homophobia. “What kind of a man would want to engage in that?” Meanwhile, there are a lot of men who consider themselves straight who sexually engage with other “straight” men under particular circumstances.
I recently learned that contrary to what I had always heard/thought, ancient Greek men didn’t always have anal sex with boys. It was often an odd kind of fucking between their thighs because penetration by a man was considered unsavory since it essentially made you into a woman. In other words, this belief about men having sex is extremely old and well-entrenched.