I dunno if this is really some high modernist plot to assimilate all of these quirky little polities into a single transportation regime. If New Mexico or Montana don't want trains I really couldn't care less. But the actual power dynamic is the inverse of what you're positing: the western states elect senators with frontier mindsets who value austerity and self-reliance (nevermind who is paying for the interstates that crisscross their states) and they exert an outsize influence on policy for the rest of the country. "Santa Fe therefore Jamestown" is actually a fantastic summary of how federal transportation policy has been standardized over the last seventy years, using the sparsest and least geometrically constrained places as a yardstick for what should be built (freeways) and for whom (people making 20+ mile city-suburb or suburb-suburb commutes).

> The problem is that geography and history make the US unsustainable over the long term.

Here we agree, which is why the US should build several dense intercity rail networks within its borders which will eventually serve as skeletons for its balkanized successor states :)