It’s not that simple. For trains to be a complete solution you need walkable cities, and high density transport-oriented residential construction near stations.
This is almost diametrically opposite to parking-oriented cities and sprawling suburbia.
Suburbs are often plenty dense for great transit if you give great. Howeveriwhen transit is as bad as most get it is no wonder nobody uses it
The best time for a city to invest in making their city walkable and public-transportation-able is decades ago. The second best time for a city to invest in making their city walkable and public-transportation-able is now.