More than three quarters of Americans live in suburban or rural areas. If you tried to run an hourly bus down a suburban street in the middle of the day, it would have one passenger. You can't run bus service at the density of the suburbs, with single passengers it's just a slower, more expensive and less efficient Uber.

Then you get traffic congestion in the city because those people come into the city in their cars. But you can't just add mass transit where the traffic is because those people still need to traverse the part of their path where it isn't.