Big Red 'L' - I think they're trying to prove what L33T H4X0R5 they are and how many B0X3N they can 0WNZ to fuel their pathetic little egos as none of them will ever do anything good or worthwhile in their entire lives.
BEagle - The problem is that the virus sends out more copies of itself, so the odds are the person who sent it to you doesn't actually know they're doing it, because they ran the attachment when they got the mail from some other, possibly equally innocent, person. Tracing it back would be incredibly complicated. The person who started it off probably used an anonymiser to cover his tracks (and it almost certainly was a him - some pale spotty geek who needs to get out more).
BT Openworld now do virus checking on all mail passing through, and this has caught a lot of viruses before they've ever got to me. They also do spam checking too, although a lot still gets through. If all ISPs did virus checking, in close support from anti-virus companies, and blocked any viruses passing through them, it would do a lot to curb the spread of these email viruses.