>>15250951. There's 500 Amtrak stations in the US and only a handful of them are high level platforms (almost all in the Northeast). Most are literally just a rickety old building with a ticket window and if you're lucky a cafe, a parking lot, and a slab of overgrown concrete next to the tracks.
2. The majority of Amtrak rolling stock (Superliners more specifically) are completely incompatible with high level platforms because their doorways are too low. To my knowledge, only Amfleet, Viewliner, and Acela are compatible with high level platforms and that was because they were almost exclusively intended for service in the Northeast where most of the major cities already had them when Amtrak began service.
Even one of these would prohibitively costly to replace, but both of them? The costs would be astronomical.
Amtrak's got a LONG list of problems, but low level platforms is pretty low (pun intended) on that list.