BART from Oakland to SF is OK. BART to Caltrain to Silicon Valley is a proper hassle. The two systems don't line up real well, you're liable to clock 4 hours a day commuting if you go all the way down to Palo Alto. Driving at an off-peak time is strictly better.

Oakland is a big place, and the BART stations are generally either downtown, where the rent is relatively high, in places you don't want to live, or far away from you.

You don't think people already do this?

I know people already do this. My intent was to ask why it's not the default for people who would save $1-2k every month. It seems the assumption is working in SF means living in SF for software developers making > $100k/year.