Building a train system to connect a few cities across an undeveloped nation is infinitely easier than supplanting an established local road system. I'd go so far as to say replacing the current interstate system would be easier than replacing all local infrastructure that was built up around cars. Live outside a big city and see how communities and businesses are structured. Now think of the logistics involved in ensuring all of that continues to have access. Not to mention you have to convince the general population that they are going to have to walk a lot more and good luck convincing families with multiple children that have multiple places to be at nonstandard times.

It's just one of those areas that is incredibly hard to replace. Maybe it isn't impossible. And that'd be great. But beyond the hurdle of the task itself you have to find a way to get mental and community buy in. It can't be forced on everyone.