It’s pretty disingenuous to claim that your city founded in 1300 has tight streets and isn’t car-friendly because people in 1300 were really big on public transport.
And the answer is that cities grow descriptively rather than prescriptively. They generally add what is in demand/what they need piecemeal, and most US cities really grew in the 20th century.
That’s why NYC, for example, has significantly better public transport than most of the nation - it’s one of the oldest cities
This is also why moving to mass transit is a hard sell. It’s expensive and there is less demonstrated need and more forethought behind the switchover.