I agree. A lot of this stuff is a function of age and marital status. Older people tend to get married and have kids, and once that happens they clearly prefer the suburbs.

There are many folks who prefer city life, but I bet they would be found in much greater numbers in the 'real' cities: New York, Chicago, Los Angeles, Dallas, Houston, Washington D.C... San Francisco just feels like a slightly overgrown town with hardly any cultural amenities one would expect from a world-class city. It does have almost unparalleled access to very pretty coast, woodland, and desert all in three hours' range, though.

40% of SF residents are married. That is just slightly lower than nearby mostly suburban Sonoma County at 47%. And the median age of an SF resident is actually higher than the state median.

How many with young (K-12) children?

I don't know what exactly you consider "city life," but Los Angeles does not come anywhere close to San Francisco by my definition.

The second-class treatment of public transit over car-driving alone is awful. I don't have to worry about being stranded ANYWHERE in the bay because I didn't finish what I was doing by 5pm, unlike my last trip to Santa Monica.