Really depends where their job is. I wouldn't be selling my house or moving apartment just because I got a new job, so I could walk there instead of just driving. Just because someone lives in a city, doesn't mean their job is right next door.

For the aditional 20% who can use busses, the problem continues to be travel time. Fx. I could take a train, and a bus to get to work. But it'd take about 1 hour. I'm in country with a comparatively great public transportation system, but I can get to work in a car in 15 minutes instead. Sure, if you get anough people to switch to public transportation, maybe you can run more buslines, because there'd be enough people to fill those lines, but you'd need an astounding amount of lines to avoid people having to switch busses, and wasting time by not going a direct route. I have a car because I'm not going to waste 1,5 hours per day on transportation.

The problem is convenience. If the transportation system isn't at least as convenient as a car, people won't use it willingly. They'd even pay a premium to avoid it. You can force people by banning cars, but good luck with that. We've seen how the french react when a few speedcameras are installed (Spoiler, they burn them).

I want car-free cities, with the exception of transporting goods and work that absolutely requires a car. It'd be utopic! But I just don't believe we can cater enough to everyone's needs in any kind of satisfactory way, without going completely authoritarian and removing people's ability to live and work where they want to.