MUNI routes are not optimized for all people and some people work in a different municipality, etc. Academy of Art College, UCSF, etc. all have private buses and shuttles to address that shortcoming. I can almost hear the outcry that 'techies' are overcrowding our buses!

Because Muni is incredibly slow--I can walk from Fort Mason to Market Street faster than I can take a bus, and that's with a foot injury that has me limping and unable to stand by the end of the walk--and doesn't go anywhere useful. Caltrain is slow and expensive, lets off a several mile hop from Google, and requires an hour or more on the aforementioned awful Muni bus to get to the starting part.

If the public transit was functional, like in DC or NYC or Boston, we'd use it.