Of course the difference is vast, I think you could compare one part of NYC with NYC even and end up with vastly different ideas of trash. And that's kinda what I am going on about; the trash under highways in some part of the city is a meaningless metric.
I was flying from NYC to Denver a few months ago and a Denverite and I struck up a conversation on this very topic after observing multiple people throwing trash on the floor in LGA. Speaking of which, Denver, another city that is much cleaner than anywhere on the east coast.
I guess I’m saying something a bit different. When people visit SF from SFO they get on the 101 and within 2 hours they have a feeling of things are broken and that memory sticks. I’m desensitized to those problems so I mostly see the beauty.
If people land at SFO and took 380 onto 280 thn straight to golden gate perhaps their impressions would be different.
The homeless problem is very bad in California and SF in particular, and it is very concentrated in a small area to the east that looks positively dystopian. But that doesn't represent the whole city. If there is a next time you visit, I recommend spending some time in the panhandle, the Haight, the sunset, basically anywhere bordering golden gate park.