I think this is the same for every major american city. I don't know how is Chicago, or LA, but in NYC for sure nobody is saying hi to random folks. The only time you say hi is to old neighbors (which are few, as people move in and out often), and to the coffee place/restaurant/bar you frequent often.

NYC does have plenty of homeless as well, but the cold clears them up pretty quick. By late November, NYC is too cold, and during the summer it can get too hot.

SF definitely has other major problems. It is just too lenient on crime. NYC has seen somme uptick as well, since last year (pre-covid), and the culprit might be the no-bail reform. While might seen progressive in nature, it is letting out folks that have done multiple crimes back to back, and they return doing the same. SF has implemented this earlier and the uptick in crime is reflecting it:

There was a guy that got arrested 14 times in the last 18 months for car theft. And he is still free: https://twitter.com/SFPDTenderloin/status/133728051660988416...

When you have car-thieves/robbers running free around, immagine all other lower level of criminals. They know they can operate with impunity and they act accordingly.

Ps. (I lived in SF for 7 years, and now in NYC for 6 years. NYC folks are less friendly in general, and more direct. SF-ers are more polite, but also more flakey).