Corridor Rail owns most of them and has been trying to find interested buyers for years now, offering to deliver them in a completely refurbished "zero-age" condition.
Corridor Rail Development
If Amtrak was serious about expanding passenger service on an accelerated timeline they would give this serious consideration. But, they aren't, and so they won't. They'll fiddle-fart around for a decade before the next gen equipment comes online. And that's if things go well. There is a very real chance that funding gets clawed back and Amtrak will have let a generational funding opportunity slip through its fingers.