Even if you built such a thing, it wouldn't get much use. People just don't like to walk that far, even New Yorkers. The GW Bridge gets about 200,000 pedestrian crossings per year, compared to 100,000,000 vehicle crossings per year. Put another way, more vehicles cross the GW every day than pedestrians do in a year, almost 40% more. Even if a JC - Manhattan pedestrian crossing was somehow an order of magnitude more successful than the GWB and managed 2 million pedestrians per year, it wouldn't make much of a dent in the 14 million vehicles that go through the Holland Tunnel, 19 million vehicles that go through the Lincoln Tunnel, or the PATH's 34 million annual riders.

There are just much better transportation investments to make.