Disenfranchised kids with nothing else going on in life and wanting to belong to something larger than themselves.
None of this is new, same reason people became hooligans back in the 70's-80's
Just to expand on my light-hearted previous comment.....
Match ticket: £40+
Coke: £50
Beers: £10 - £30+
Transport: £5-10 +++ (depending on where you live.... Triple that or more for an away game.)
Every one no doubt with a top end smart-phone on contract in their pocket
Doesn't add up to a deprived working class youth to me.... More like a bunch of privileged brats that really ought to be able to fund something more constructive to do with their energy.