Amtrak California which runs to Auburn is not Amtrak. It is Capitol Corridor service operated under contract by Amtrak. It is unlikely that the Capitol Corridor JPB would fund service in another state
I am surprised that Amtrak California wouldn't consider some sort of regional Amtrak train(yes I know it's contracted) to Reno and also Las Vegas, with how many Californians travel to those nearby cities in NV. Truckee seems like a popular town for a lot of people to visit, so it's slightly surprising to me that they wouldn't at least consider an extension of the Auburn train in each direction to also serve Truckee.
I do wonder if Nevada did an assist with funding, if service could finally occur? There probably are issues preventing this from likely happening, that I don't totally understand.