Have you seen the state of SF public schools lately?
- https://www.sfusd.edu/about/news/current-news/SF-Board-of-Ed... (which is clearly more important than https://www.sfusd.edu/services/health-wellness/covid-19-coro...)
- https://twitter.com/hknightsf/status/1359382113875755011
- https://www.sfgate.com/education/article/sf-school-lottery-L...
I think your idea of "rich parents funding SF public schools" would probably be rejected by the school board, so for most it's not even worth trying, given the proliferation of high quality private schools nearby. And even if the school accepts it, the community won't.
Say what you want about Zuck, but he donated $75M to the only public hospital in the city and they don't even want to keep the building named after him and his wife (who worked there no less!). Comically, they can't actually do anything about it, so they stick to meaningless non-binding resolutions.
Therefore, if given the choice, those who can are much more likely to spend 30-50k/year to send their kids to private HS than to try and go through the process of dealing with the city government. I assume that dealing with Cupertino/PA/etc. is frustrating, but not nearly as insane as SF.