Uh

It's not usually that people don't like shōnen ai. It's just that most shōnen ai has no sex scenes, and people are horny and like their sexy scenes.

Generally, from what I've gathered, people don't really hate shounen-ai. The fact that there's better plot and chemistry between the characters in a shounen-ai manga simply makes people want to see them do the deed with more intensity than a yaoi manga, which, often, has a comparatively drab storyline and character. It's just that.

really who? if it pertains to the comments below, it's the demanding/greedy readers who asks for more in shounen ai, not the mangas.
and yes, shounen-ai they had great stories most even better than yaoi so there's more best sellers in the shounen-ai area than yaoi mangas AFAIK.

Haven't encountered someone who hates shounen-ai here. It's just that some are disappointed because there's no sex scenes. Personally too, I prefer shounen-ai than yaoi because most stories have great plot and characters especially the realistic ones. But still, I love them both (≧∀≦)

Shounen ai will become more popular if sex scenes is added in atleast last few chapters of the manga.
I suppose.

there are shounen-ai that has sex scenes in it. the only difference is it's heavily censored, unlike in yaoi. btw, in japan there is more shounen-ai that is very popular in compare to yaoi. yaoi is kind of like targeted for a specific crowd, unlike shounen-ai that has broken through mainstream.

I think, the reason why shounen ai is more popular in Japan is also because buying shounen ai mangas with less sex scenes is less embarrasing(don't take it too literally) than buying yaoi manga.
Don't take me wrong. Its just that reading yaoi manga online is lot easier. I suppose that's why shounen ai is popular in book form while yaoi is popular online.