Because people in hoodies stab you. /sarcasm
To be fair, they're going a bit out of fashion. I wear hoodies every now and then, mainly when I'm just lounging around wasting time on the Atlas Forum.
i've noticed that too a little, but the whole chav hysteria seems to have actually been dying off as a whole in the last couple of years, probably due to the economy. i remember it peaking around 2006/7
I do think the link between hoodie and chav has put people off. But Hoodies often make you look scruffy aswell, that's not the thing to be in metrosexual Britain.