alt Hacker NewsSF is quite small compared to the other cities you mentioned, both in land and population density, and is quite a young city in comparison. The beats and hippies were a flash in the pan. They left a mark, but many dispersed rather quickly, and the rest have been ironed out for many decades.
The exact same thing is true of smaller cities like Pittsburgh, as well. The point is that their cultural histories still manage to exist today, even at some level, whereas tech has turned SF into a historical culture-free zone, entirely detached from what SF was even 25 years ago.