People making individual decisions. All else equal, we'd slightly prefer to have people in NYC, because we think the in-person time is a plus for the casual interaction that happens in between "getting things done". But we've set our selves up to make real work and official team collaboration work almost entirely online. We've learned that the in-person benefit is more than outweighed by how much you get from being able to hire the best talent that loves the product anywhere, not just the ones willing to live in the city you happen to be in.

The most common reason for someone going remote (that I'm aware of) is starting a family. New York's great, but spacious it is not.

I can think of 3 devs who have gone remote, and 2 devs (including myself) who have moved to NYC since I've been here. Most people stay wherever they were hired. The only location-specific policy I'm aware of is a cost-of-living adjustment in NYC (though that may also apply to London/SF/etc., I don't honestly know).