It will take decades to achieve significant modal shift.
Decades have been spent building for cars - sprawling housing estates with density and road layouts unsuitable for buses, out of town shopping, workplaces on the edges of towns spread over wide areas.
Public transport can not provide for this.
Sure many young people manage without cars in the cities. Then they have kids, move to the suburbs, and need cars.
I don't love in a city, in fact I love in a village of 8,000 (very much the sort of place which people with families move to away from cities) and with some small changes (see previous post) we could live without owning a car.
Just because people think that they need a car they have a car (or more cars per household), if you actually consider what you would need to do not need to own a car then you could be surprised at how little you'd need to do to reduce the number of cars that are within a household. Maybe even down to boot owning a car at all.