Blame it on New York all you want, but you're stuck with it, lol.
20 years ago, it was called the "Brooklyn accent." Since the hipster douchebags have taken over said borough, it has become the "Jersey accent."
BTW: I hail from Lawn Guyland, where we REALLY speak with accents (see Jerry Seinfeld and Fran Drescher, to say nothing of Islip's own Edie "Carmella Soprano" Falco). My parents are from NJ, and I spent a few years living in the Princeton area. I know of what I speak, even if the Hollywood/Manhattan axis of evil doesn't.
Besides, if you really want to sound mentally challenged, go to South Boston and try to imitate the locals.