I think its just an attitude that goes back to when freeskiing and especially park skiing was starting up, any sport that is not generally accepted and especially so called "extreme sports" like freestyle skiing will try to be different and stand out as a kind of cultural movement. I know that not all of the original park guys dressed like this, but the whole skiing scene is based a lot off of edits, pictures and generally watching other people. As many of the pros adopted the style (and I think a bit of it was borrowed from snowboarding at least at first) people wanted to emulate them. As a result, a "look" evolved and continued to evolve as wearing something slightly brighter or baggier than the next guy may help to get more attention for your edits, pictures and from people on the hill. And now here we are...
Personally, I don't rock huge clothing. I like my fit a bit baggy but not "thugged out" like some kids on here. honestly its just a part of the culture so don't worry so much about it and do your thing, thats what freeskiing is all about.