There's speculation. Some say it was the phone call(s) by The Kings lawyer(if it was a real paid lawyer). Some say he recieved too many threats. Some say he was silenced.
My theory is that FlashRob evolved and fatherhood humbled him. Not to mention...he's really into his band so that keeps his mind off wanting to cast OWNINGs as he see's fit.
two things happened. the first was the insanity with the mattT battle where his entire background and that of his family was revealed all in one fell swoop. he really got someone and they PM'd mattT rob's name, address, phone number, business info, wife's info, i think his parents, and then linked to some really damning posts he'd put up and implied that people should email them to rob's wife. real sick.
the second was that he had a kid. i have a feeling that simultaneously watching how the internet can transform from fun time to serious problem in the blink of an eye plus realizing he has a child in this world to take care of really re-aligned rob's priorities.
to the people complaining that he doesn't "own" people anymore, realize he has a family, a child, and is running his website business well enough to live off of it. i heavily doubt the guy gives a good god damn about making silly little animations any more.