Health insurance is a fairly competitive market - narrow profit margins, commodity good, many competitors (in most states, including NJ). If a health insurance company can raise prices, it's probably because costs are going up or are likely to do so in the near future. The calculus is fairly simple:

If I raise prices, my competitors don't, and costs don't go up, I lose customers.

If I raise prices, my competitors don't, and costs go up, I lose competitors.

Insurance companies all seem to be placing their bets on the latter case. If you feel they are wrong, feel free to bet against them.