A few thoughts crossed my mind One, some sort of law prohibiting imports of magazines. Two, strict licensing requirements to be allowed to ship and/or sell in NJ and it's not worth the pain for the companies. Three, companies don't want the hassle of learning all the ins and outs of states that have tight gun laws and don't want to face possible litigation for shipping a mag that may violate capacity laws or be for a prohibited gun. So they just say "No Shipping to _______". Again, just thoughts, no definitive answer.