So when you said, “I know many families” you actually meant “here is my anecdotal experience?”
Recall that SF isn’t that big a city - only 800,000 people (and with a low %age of children to boot) - so there aren’t that many schools in the city.
[edit] it’s also the case that the only variation in response was on the private school side - SFUSD took a monolithic approach to their schools (which are the greatest in number and have most of the students in the city)