We do not have a population three times that of the 50's.
It was an exaggeration (though it's actually true of world population, amusingly!).
Public transport can and does work in various parts of the country. Central Scotland it is fine. Cheaper, easier and not too much slower than a car in the main.
TJ, I live in central scotland, it's not cheaper or easier than my car. A return trip on the bus takes nearly 1:30 and costs around £4, goes every hour and means I have to walk half a mile at one end and 2 miles at the other. My car takes 25 minutes, leaves when I want it to and costs around £1.50 fuel and 50p parking. I can cycle to work faster than I can use public transport, and thats from a commuter village.
There is no shop in your town – why? 'cos all the car drivers shop elsewhere so the village shop is unviable! and so on and so on.
There are still shops in my town. I shop elsewhere because a local shop can't carry the diversity of products that I want.
It took a generation or two to get into this state. It can be reversed in a similar time
Not without people making large sacrifices in their standard of living, which they will naturally tend away from. You see the thing is I believe I'm odd 😆 , I could happily live in total isolation (see the BBC olymic trek thingy last night, I'd love to live in one of those remote villages) but when it's perfectly viable to have the comforts and when you don't have the lovely natural beauty and nice community spirit to go with the negatives of losing those comforts, people will never tend that way, even if the costs are vast.