I think it has alot to do with what is available. Yaoi, which yes is my favorite, has pretty much flooded the U.S. market. Almost everywhere you look, you can find yaoi or shonen-ai. Yuri, on the other hand is less available. My friend Heather was just talking to me about how she can't find more than one or two Yuri manga and anime. She's pretty upset about it, too. I don't care for the Yuri myself. People tend to get more into what they can get their hands on. I also believe that yaoi fans are more vocal about it. I don't really know but that's my guess. Personally I just like looking at the pretty bishies and it's romantic.
