This really is nonsense but somehow every time this topic comes up people being it up. The size of the country or its population density is not really relevant.
People in Europe dont take a train from Greece to Sweden. They fly. In fact most fly Vienna to Amsterdam.
In the same way somebody from New York would definitely fly to LA. (They are not driving now btw)
That doesn't preclude the existence of public transport connecting NY to Philadelphia. It also does not preclude NY from being walkable! Or bikeable. It doesn't stop NY from having good public transport! It doesn't force you to drive to work in NY.
This is much more about local policy.
Different solutions at different scales!