I'm talking LARGE amounts of zombies. Nuking Manhattan vs nuking Staten Island.
In Manhattan there are ALOT of people compared to Staten Island, a suburban area (sorta kinda pretty much). Yes, there are people in suburban areas. Are there enough people to bomb it? No, it's a waste.
In reality, if a zombie apocalypse where ever to occur (never) it's unlikely that Nuclear Weapons would be used in highly populated areas unless the infection is limited to that one area. The fallout and overall devastation wouldn't be worth it.