I think this is true, but it can't explain most of the difference by itself as most of the major wealthy cities I have been to do not have anywhere near the sca

I think this is true, but it can't explain most of the difference by itself as most of the major wealthy cities I have been to do not have anywhere near the scale of homelessness and mental health issues as San Francisco. (I say this as someone who has lived in the UK, France, and San Francisco (albeit briefly). I really think the local people (I don't mean you here) have a kind of blindness to the problem in San Fran, perhaps because after a while you start forgetting how abnormal it is. There is so much wealth in the city but clearly not enough people commited to acting.