Cars are just more precise in space and time. In a car you go from your origin to your destination, within lot-to-door distance, and you go exactly when you want to.
With public transportation, you travel a block or two to enter the system, arrive a block or two from your destination, and you can only leave at certain intervals.
At my last job the commute was:
10 minute walk to the bus, 50 minutes on the bus, walk across parking lot to office.