Because Sacramento is hot, suburban, and has limited employment options.
And Napa is dry, rural, and has no employment options.
SFBA OTOH: Temperate, verdant, urban, and swimming in jobs.
I do like Sacramento and Napa. But they are very different lifestyles, despite being so close.
Also, it's very difficult to build in Napa, due to water availability. Sacramento is easier, and it gets even easier as you get farther out...but fewer people want to.
Napa County has acute water availability problems. SF County and most of Alameda County (the most populated parts) generally do not.
I didn't say Napa was hot. Sacramento is hot.
But SFBA comprises a large area and large climatic variations. I don't think it's meaningful to consider all 9 (or 13) counties in comparisons, because all things become true. Cold, hot, humid, dry, windy, placid, densely populated, sparsely so.
If you're asking why SF is SF and Sacramento is Sacramento, then I don't think there is a satisfying answer. If you're trying to lead me to a preexisting conclusion, I'd prefer that you just engage directly.
The thing is, climate doesn't matter. Vegetation doesn't matter. Good looks don't matter.
All that matters is proximity to jobs. Sacramento doesn't have a lot of them (although that is changing now), so it's not attracting significantly more population.
Taking it further -- all that matters is proximity to trade routes. SF has (had) a port, and so it grew first. Jobs resulted. The effects were compounded over years.
Sacramento has a river. The river is why Sacramento is not Vacaville. Also, it was selected as the state capital (partially for the available and inexpensive land!), which has greatly accelerated its growth.
Sacramento is the fastest-growing city in CA. It's actually almost as populous as SF, though of course much less dense. And the job market is good, but the jobs are not the same kind as in SF (and fewer are applicable to the typical HN denizen).
I really don't know what you're going for here. Different places are different, for myriad reasons. It's not as one-dimensional as you seem to suggest.
And Napa is dry, rural, and has no employment options.
SFBA OTOH: Temperate, verdant, urban, and swimming in jobs.
I do like Sacramento and Napa. But they are very different lifestyles, despite being so close.
Also, it's very difficult to build in Napa, due to water availability. Sacramento is easier, and it gets even easier as you get farther out...but fewer people want to.