[gozur88]

I don't know if it's true for SF, but some cities have noise ordinances that pretty much shut everything down by a certain time.

As others have noted, people who have the sorts of jobs that put them behind a register can't afford to live in SF, and public transportation shuts down at midnight or so. If you were working a restaurant it would have to close by 10:00 so you had time to clean up with a little buffer to make sure you were on the last train.