It also won’t be widened because an inland collector route for local traffic already exists and is pretty wide. El Camino Real.
As far as the NJ towns, the area is actually pretty built up, but the houses have tended to not turn over as much as in CA, so they stay in families that have homes either in NY or further north. There are some retirees and recent immigrants who live year around, but the population ratio summer to winter is something like 5:1 or higher.
The “nicer” part of the shore is also not nearly as convenient to get to from NYC as North County is from San Diego.
