One of the biggest is that people actually like living in suburbs, and they could afford to do so after WWII.
The promise of the suburbs is a detached house, with some private outdoor space like a back yard, in a quiet area: essentially what the rich had always preferred and been able to afford. That lifestyle became broadly available to the middle classes after WWII. It's hard to blame people for wanting that.
People still like living in suburbs. They still like owning cars. They still vote against new transit projects for a lot of reasons, but the biggest reason is that they don't want to pay taxes to support a system they would not use themselves.
So I just don't buy the idea that the National City Lines conspiracy caused our current automotive culture. I think we would have ended up with the same car culture anyway, because huge numbers of people wanted to live in the suburbs.