Oddly, NYC is archipelago city, and the only way from Long Island/Brooklyn/Queens to New Jersey is via Manhattan, hence the congestion. I guess one could take the huge detour via Staten Island, but the Verrazzano already has a big toll.
Considering that the Cross-Bronx parkway is the road with the worst traffic in the entire country, you can't "easily" cross the GWB (but you can do so after sitting in traffic for several hours). And the privilege of this traffic nightmare is a $17 toll for the GWB ($13.50 if you have EZ Pass).
If only the roads were planned bit better.