Because they're chavs and are ******* idiots. Apparently its to simulate that they are carrying a gun - gangsta rap style: what these breathtaking idiots don't seem to realise is that they are not black and they are not from LA. They are spotty skinny weedy little buffoons from some little **** pot council estate in Droitwich.
I have the answer:
Because Leeds is so close to Bradford, where all the men are so scratty that they can't get girlfriends, and therefore have to errm... fulfil thier own needs.
(Don't have a go at me for badmouthing Bradford, I live there...)