Well, I didn't make the distinctions. Usually really gay men hate yaoi and don't want to be seen dead near it. If they read manga, it's either Seinen like all men, or bara. Even if a part of them would prefer the guys to not be soooo exaggeratedly huge, bara is still the only gay comic that real gay men can watch without cringing. Yaoi and Shounenai is meant for women, to fantasize over men behaving like girls.
I'm not saying it's meant for gays, I'm saying on average, gay men don't like yaoi and shounenai because it isn't manly enough, and bara is. Is what I hear most gays I know say. And the yaoi and shounenai is really meant for women, you know. That's why the mangaka mainly draw it.
Bara is usually drawn by men, yaoi and shounenai by women mangaka. That too makes a difference.
Bara is literally in it's entirety smut, yaoi and shounen ai have more story. If they're saying they prefer Bara because "it's more manly" in those words specifically they're probably talking about which genre holds the most sex appeal to them. The girly bottoms in yaoi are annoying, but that's just a matter of the quality of the yaoi. They're too different to say Bara is "better". It's like saying a fork is better than a spoon, they're for different things, i don't go into Bara expecting story.
Better? I'm not saying that. If the drawings are good, and the plot and the characters are good, then it's good. I'm not into "what's manly enough" or not. I'm a comic drawer myself, so I look at the quality of the art and that of the plot. But most people look at manga for emotional and subjective reasons, not for artistic quality. Like for girls: they love yaoi because the bottoms in there behave like girls, and the tops like the men they dream of meeting themselves. I've asked many girls and they all say it: "AA if real men would act like they do in yaoi manga!" swoon swoon, you know? :-D
So I suppose if other men like to read manga that are not like that but more pleasing to macho personalities, then that's their taste.
Also, I have read some bara manga that were not at all hentai, but real stories. So it's not like all bara are porn.
yaois should have more reverse roles.