To get to work by 8AM, I would have to walk 3-4 blocks to the bus stop leaving by 6:40AM (not so nice when there's 6" of snow and -15F temps or when it's 90F+ at 7AM). I get on one bus to go about 2 miles away, then wait 15-20 minutes for another bus to get downtown.
Leaving work at 5PM, a 5 minute walk to the nearest bus depot at work MIGHT catch the 5:05PM bus, otherwise it's a 30 minute wait, then another transfer to another 15-20 minute ride and a 4 block walk uphill to home.
I could drive even with 7:30AM/5PM traffic in about 20-30 minutes either by Interstate or by a major through town federal highway. So I can give up an extra 1-1.5 hours a day of my time and walk several blocks in quite likely to be less than pleasant weather, or I can drive my car and pay about the same amount for a monthly parking pass as what a monthly bus pass would cost. Due to having children, I couldn't give up the vehicle, it would just mean different routes for the car and the bus.
Having visited cities like San Francisco, New York, Houston, and San Diego in the last year, cities that have well developed urban centers with public transit in mind seem to do much better with this than ones that were designed around cars and are trying to retrofit mass transit into them. The biggest difficulty in getting around NYC was figuring out whether to grab a cab, get on a subway, get a bus ticket, or get on one of the multiple trains. In several cases, there were at least 3 different options to get from A to B in roughly the same amount of time, though prices varied quite a bit. Subway was cheap, trains were pretty cheap, cabs were reasonable only because of the short distances.