Why in NYC and not Seattle/SF?
As to why we were living in New York, I can only answer for myself, but here you go: I grew up here (city and suburbs), most of my family still lives in the area, my friends live here, and I love the energy of the city. It feels like home.
If he wanted help/sponsorship running SF or Seattle, I'm sure he could find it, though.
I actually think Hawaii or Thailand would work -- you could get a few cheap house rentals on the big island, with minimal distractions, and do it there.
SF to Hawaii flights are $300 r/t. If it were in a place like Boulder or Utah, you might be able to get local companies/VCs to sponsor it, though.