I think I have a few reasons. Most of them could be attributed to the heat from LE.
Like Bunyon, I think a lot of guys in NNJ don't mind taking a trip into the city for action. There are plenty of providers, most places are open late and it is very easy to mix in with the crowd. In NNJ, if you go to a hotel or massage parlor, it is very easy to feel like somebody is watching you and knows exactly what you are there for. Not to mention the police in the suburbs of NJ always seem to have a hard-on for catching johns. In NYC, if you walk into a building, you're not looking over your shoulder as much as you would in NNJ.
Another reason is that there are lots of full service places in NJ that don't advertise. They may have put an ad in the Record years ago and have kept in touch with their clientele since relocating or being busted. A lot of these places may have recently placed an ad for a week or two just to let their regulars know they're open for business again. Once the word gets out to just enough, they stop advertising and go UTR.
It's been a while since I've tried a new place in NNJ. Most of the places that I see advertised in the Record have been advertising for years and have always been targets of police in their towns or known to give shitty service (Heavenly Exit, Ritz, place in Totowa on 46, etc.) The only place I've been going to on a regular basis has been a place that has been in business for over ten years and used to advertise years ago. They were busted once and relocated about half a dozen times. I've approached them to advertise on here but they don't want ANY exposure. I think that many places are choosing that route based on the penalties if they're caught. Another place that I've tried advertised about a year ago and have since stopped advertising. I reviewed them on here twice but it may be hard for guys to get in because now they supposedly dont' accept new clients.
I really think the combination of precautionary measures on the part of the "better" establishments and the search for an alternative venue in a place close by such as Manhattan have made this market very tough to crack if you don't already have an in. I mean look at CNJ and SNJ and it seems like things aren't as bad for the places in those areas. Maybe it's because the johns can't travel the distance to Manhattan and still frequent the places in those areas no matter the risk or price of services.