Plenty of things were major issues in SF well before they diffused to the rest of the country. It’s why the American right is so dead set on villainizing SF’s progressive government:

LGBT rights, recreational drug use, Nimby-ism (to your point), Internet socialization/commerce, rejecting elevated freeways, freely moving between jobs multiple times in a career (see: The treacherous 8), voting by mail, bicycle commuting, living alone/not having a traditional family structure.

SF is a place full of wealthy college educated people and as the saying goes “The future is here, it’s just for the rich.”

I’d argue that national trends around a drug use, housing policy, family structure, and Internet usage (phones make being homeless way better than before) are going to make homelessness much more common everywhere, SF is just at the frontier.