It's not that easy. For one there is a notable population which will complain and even for those who want to get rid of cars it is a long project: You need to change the city structure. If you have a resedential area without shops to run errands and no workplaces whatsoever people will need to travel long distances each time. Long travel time (whatever the means) means that you don't do grocery shopping for a day or two, but a week or two, which means you carry more and that's only viable by car.

Transforming city structure and society takes time.