I assume you are referring to non-Asian guys (i.e., white/or western guys, etc) who like Asian girls. So, let me rephrase your question: Why do so many Asian girls like white/western guys? Knowing the answer to this question may help you understand the answers to your question. This subject is extremely complicated, and there is not one single reason or answer to explain it. If you want to know why some western guys like Asian girls, and why some Asian girls like western guys, I'd be happy to discuss this with you in more details by email.

They have beautiful smooth skin and very feminine features, usually are very slim, and the whole "exotic" thing doesn't hurt either

I don't know. I think it just depends on who they are. Maybe because they are deemed exotic or something. Although, I really like asian guys over white guys.

They're called "asiaphiles" - you can use this word to tease them. ;) I think it's a case of "the grass is always greener..." so some (non-asian) guys think Asian girls are automatically better because they're not like girls in their own country. :-?

I agree that its the "exotic" thing. But generally its just a preferance that some people have. When looking at the big picture, most people marry within their own culture; asian or not.