There aren't a lot of good places to put them, at least in the Bay Area.
The Bay Area is mostly low-density sprawl. Pretty much anywhere is a fine place to put it. The problem is the veto rights small groups of people have over projects with regional utility, i.e. there's no way for 9 cities to over-rule 1 city for something that benefits them all.
Watsonville has an airport with plenty of room to better serve south bay and Santa Cruz.
Moffett, of course.
Even San Carlos has an airport with a fair amount of general aviation traffic.
Hayward Executive always looms when I fly into Oakland- it looks more than big enough.
Livermore, Novato, Palo Alto (busiest general aviation airport in the country), the list goes on.
Frankly just getting Concord back into the act would be tremendously difficult. My definition of "good places" differs somewhat from those in power, but that may slowly be changing.
As a result, you experience crowding in SF even before your SF-bound plane leaves the gate or takes off due to air traffic control ground holds. Epic delays then cascade through the rest of the air traffic system, delaying wherever that plane was supposed to go next.
This could all be alleviated if they moved one their runways further apart. I get that NIMBY's won't let them fill in more of the bay to achieve this (c'mon guys, what's another 40 feet or so?). What I don't get is how it doesn't seem to occur to anyone to move the terminal and gate structures back "west" to make this space. After substantial renovations on Terminals 1 and 2 for what is still mostly a ranch-style airport, you'd figure they could do something to free up some space.
And don't get me started on SF's slowmobile, taking you to the rental car center in 10 minutes or more.
3 hrs peak times on the weekend
3-4 hrs rush-hour commute