Not sure I follow. If the homeless aren't coming from elsewhere, then the "ease" would have to be that people on the margins would be choosing to be homeless instead. However, if that's the case, then why would NYC be immune to this effect? After all, they have way more shelters than SF, rents are just as sky high, and SF residents typically have a higher income than their NYC counterparts meaning there should be fewer people at the margins.
Or maybe the easier it is to end up homeless, the more homeless you get.
Between wages and housing costs, it's unclear to me how ~half of SF isn't homeless.
I'm not sure people whose goal in life is living in a tent under the freeway exist in any significant numbers outside of the imagination of libertarians.