The problem is that you have to go all-in on transit to make people want to ride it. You need to have frequent, reliable service, clean trains/buses, and feelings of safety. You also need the infrastructure to be designed well: build subways rather than surface-level trains. If you can't build subways, elevate the trains, or at least do your best to grade-separate, and give priority to those trains at traffic signals. Buses should have dedicated lanes.
Transit in the bay area fails at pretty much all of those things. Service is just infrequent enough to make things difficult, and unreliable enough that you worry that a late or missing bus or train will make you late. Cleanliness is inconsistent, and there are often people on drugs riding around all day, spouting nonsense. We do have some subways, but not enough of them, and there is no light rail line in SF that runs only underground, so they can only be a maximum of two cars long (otherwise they'd be too long for a single city block in some areas). All of the above-ground light rail is at mercy of car traffic (with tracks in some areas actually running in the same lanes as cars), stop signs, and traffic lights (which do not prioritize the trains). We do have some dedicated bus lanes, but they're dedicated bus+taxi lanes, and Ubers/Lyfts and regular passenger cars abuse them with little risk of being ticketed.
The end result of this is that people see that it takes 10 minutes to drive and 40 minutes to take public transit, but that they really need to add on an extra 15 minutes to the transit trip to account for delays and unreliability. So even though they don't want to to deal with parking, or pay 5-10x as much for an Uber/Lyft fare, they value their transit time more, and drive or get a car ride from an app.
Earlier this year, SF Muni was experiencing a large budget shortfall. They managed to save many jobs from being cut, which is commendable, but instead they reduced service. This just causes more people to look at the situation and choose to find an alternative that will get them where they're going faster, and more reliably.
