I think he means most people don't live close enough to the city that they could reasonably ride a bike to get where they need to go.
Having all your commuters drive their car into the city is not at all a good idea. I lived for years at one heavy intersection in one of Germanys biggest cities and I can tell you, if you watch the traffic for half an hour you will see maybe one or two cars with more than one person in them.
I moved from their because the dust and the noise were having a huge impact on my health.
I don't think it is about banning cars from city centers totally. It is about finding acceptable solutions that work without forcing people. Encourage them. Have a working public transport system. Make it cheap. Make it so cheap that driving a car will cost you. Include all problems cars cause in a urban space in some kind of toll or tax.
Currently there's the commuter rail, which is hard to get to from many areas, is quite expensive, and doesn't run very frequently. It's not good enough to get people to stop driving.
There's many other factors, too, which could influence things in either way: total time spent commuting, whether you hate crowded spaces and prefer to sit alone in your car, whether you can be productive (eg: phone call, working on laptop, doing email on phone etc) or want to be able to read.
And that is the crux of the problem. Cities across the US don't have enough funding to maintain the infrastructure they currently have, let alone try to build anything new. Their only hope is to get a grant from the state or federal government.
None of this is sustainable.