@lain Because there are many people that did not fit the bill for what TV and mainstream culture thought of as attractive, ie. Hollister, A&F, etc. Nerds are an example of that, nerds used to be thought of as all unattractive for whatever reason, then some attractive nerds got on TV and showbiz, and now nerds are hot.
Nerds, punk, goth, etc. all have really attractive people. Think of how many people have it for Gerard Way or Peter Steele, although those guys would have never been hired by a A&F or Hollister.
Not because some ugly person is gonna let their hair grow and put on dark makeup means that they will be attractive though, there are still unconventional and unattractive people. Ugly people aren't unconventionally attractive (although maybe they could find a way to be), they're just unattractive.
Or think of that (amazing) movie Jennifer's Body. In that movie Megan Fox's character is supposed to be conventionally attractive, while the lead character isn't, yet most people find her very attractive if not more attractive than Megan Fox's character.
I mean, eventually people create new conventions or represent conventions less represented, but that's what the convention for "conventional attractive" convenes sorta.