At this particular moment, according to Google Maps, it would take 2hours 5min to get to SFO by a mix of bus and train, or 23min by car. Bus/Trains are cheap, but when you have more than 30 people on board you probably have to make a lot of stops that slow down the trip.

https://www.google.com/maps/dir/Googleplex,+Amphitheatre+Par...

Not really. In reality, even the buses of England for example end up driving so many trips relatively or completely empty (to provide adequate service so that you could do without a car) that they end up producing more emissions per kilometre compared to personal vehicles – you can't do that with incredibly low costs, nor can you calculate the costs by thinking of only the full buses, when that's hardly the complete picture.

I suspect that people who don't use buses avoid them because they can't choose the other 29 people who will be riding with them.