Fashion.

Who starts the trends anyway? Does it matter, or does it just give you a couple of extra brownie points when, at the pub, you casually remark that reason you wear your jeans a couple of sizes too big with no belt is your way of displaying solidarity to the LA brothers whose belts are conviscated when they are locked up. Because that is where it comes from.
Apparently.
Try telling this to the punks loitering on your local street corner and they'll probably stare at you blankly then politely ask you to move along.
My thoughts on this are exactly those of Banksy (where I learnt this titbit):
"Fuck hip hop, wear a belt".