The other reason is that the stats focus on disengagements as a result of technology failures or immediate safety concerns, and don't show the "routine" disengagements where the driver switches out of automatic mode for a period to avoid running the autopilot in situations it isn't test-ready for. Different manufacturers will likely have different standards for ruotine engagements/disengagements, and may also have different standards for what they consider a safety concern.
It seems that it would still need to work in places like SF and Manhattan though unless they get drivers to sign a contract that they will only drive in certain areas.
