I'd say the freedom of style that we're enjoying now gives birth to the desire to be a part of a group, and that might be why we do this.
I've talked a bit to my grandparents about it, and "back then" (like the fifties, sixties and seventies) everyone had the same style clothes.. EVERYONE... when bellbottoms were hot, bellbottoms were hot! Everything else was not
Now we have a whole ensemble of different styles to choose from. all perfectly acceptable.
you can make up your own styles, and aslong as they're not too outrages, people will be fine with you, and even then, people will come to accept you.
Ofcourse we grab our ideas from what we see around us, and what we see is pop culture.
Pop idols are also the first to dare to wear these extreme clothes. First of all, they are not considered human.. they are demi-gods, anything they wear is cool or atleast ok because they wear it. And as soon as we've seen them wear it enough times, it becomes acceptable and people that follow them also follow their example in clothes.
secondly pop idols want to wear something that makes them stand out. They're performers, it's their job to stand out.
and the more people follow them, the more extreme they have to get to stand out.
which is my theory on how it got to where it is now...