Agree wholeheartedly, but as alanh posted, the logistics are actually a bit more difficult with trains, since they are constantly on the move, often through very rural areas with little or no cellular coverage.

There are ways Amtrak could get around that (piggyback on the railroad radio systems which cover those more rural areas, or make sure to do all ticket processing at stations and have wired infrastructure at the stations themselves, although that would impose some potential delays when boarding large numbers of people), but all are costly and not quick to implement.

Looking forward to when it happens, though!