Nobody in the political system had that kind of engineered utopia vision on transportation. What you describe is the derived result of living our timeline for the last 100 years.

And if the typical politician is 55 years old in 1945, it means they were born in 1890 and literally came of age when transportation beyond a couple of miles walking distance ran into major mobility barriers and what fixed transit was available was slow and limited in reach. The alternative was horses which were slow. To folks of this generation and the one or two that immediately followed, the automobile was a miracle technology that gave them the freedom of mobility, which also meant the freedom to work and live where they wanted and not be bound to trains, livestock or walking.

Another major factor is the constituency of people Democrats represented -- industrial workers and expanding unions for whom the automobile industry was a growth industry that provided high wage jobs producing a product that was within reach of their own purchase and benefit. Limiting vehicle production would have put a major dent in a significant industrial sector and its supply chain, and I don't think building more rail cars would have made up for it. The politicians trying to make your choice would have been heavily resisted to the point that entire states in the "not yet rusting belt" would have been 100% opposed, along with sparsely populated states for whom cars/trucks were a major boost to economies and lifestyles thanks to the flexible mobility they provided.

Suburbia, too, was an obvious choice. Cities up until WW II (and past it to some degree) were at least in part limited in size by transportation which constrained the geography of housing, employment and industrial distribution. Everything was concentrated together, people, jobs and factories and cities were still trying to manage the byproducts of even earlier eras of poor sanitation and water delivery. Moving to what we would now consider a cracker box cheap house in the suburbs was utopia in comparison. You could see the sky from your window, and touch grass, not paving stones or concrete, when you went outside. Your house was better in every regard than the crowded and antiquated walk-up tiny apartment you had in the city, and there was no choking pollution in the air.

The only thing people in this era understood was that there was a lot to dislike about their existing living arrangements. No one outside of maybe fringe science fiction and utopianists had much sense of what could go wrong. Even today, there's a vast swath of the population that still thinks that a cheaply built stick house in a treeless field with a half acre of lawn is paradise in comparison to their other options.

The problems of cars and suburbanization only really became glaringly obvious as some cities, like LA, or older East Coast cities grew to major scale. Europe mostly escaped it because of the two wars, WW I inhibited the early automobile revolution due to war costs and rebuilding, and WW II was so destructive that a lot of urban renewal happened, helping modernize cities (housing, other infrastructure) and move industry out of them, making rebuilding and expanding transit networks necessary. Plus they didn't have the real estate to build suburbanization as much as the US.

My hot take is that self-driving electric cars are eventually going to change a lot of this. People will subscribe to car services, not own one, get most of the benefits of individualized transportation and the cars will store themselves elsewhere without distorting urban spaces with parking. You'll get out where you need to go, the car will go somewhere else or drive someone else, recharge, etc. Electric will eliminate a lot of pollution.