San Francisco why would anyone want to live there ... trashy, ridiculously expensive, smell of homeless & downtrodden everywhere, the mentally ill with megaphones shouting their crazy on the streets.

I've lived in many US cities and WoW San Fran is a shock to the system!

Because that's where a lot of jobs are. Its next to this part of the country called silicon valley. A lot of the tech industry is there.

https://en.wikipedia.org/wiki/Silicon_Valley

Also there are a lot of really nice parts that you wouldn't typically see on a brief visit, both in the city and surrounding area.

The homeless are definitely a real problem but in my day to day life I somehow manage to avoid it almost always. We don't all live south of market or in the mission.