In a patriarchy, a "real man" is big, strong, impressive, and always in control. He is dominant and he is messaged by the culture that women will fall all over him because of that. Guys who are smaller/shorter are looked at as somehow weak and having a small penis is about the worst thing ever.

It's a culture where men are constantly using dick metaphors to equate to masculinity. "He's a big, swinging dick" "Big dick energy" etc. That's men in a patriarchy comparing themselves to each other based on an imaginary metric of masculinity and I agree that it's junior high behavior but it's also a mainstream part of this culture. Porn stars are huge, not because that's pleasurable to women. Porn isn't made for women (even though some watch it) and most women find a really big guy uncomfortable. Porn stars are huge because that's what men want to see. And based on how many guys with big dicks are bad lovers, because they've been messaged that's all it takes, I'm going to say that you may think this stuff is stupid, but a whole lot of other guys are totally bought into it.