IIRC Rio Grande was already down to 3/week on DEN-SLC, which only needed one set to run, and in-season it was still profitable because of the scenery. I think that meant that the back-of-the-envelope calculations broke in favor of keeping it even with off-season losses. [Edit to add: I think there was also a rumor that Amtrak wanted to throw additional trains on the route, hence the carte blanche concerns mentioned above.]D&RGW was the third RR that did not join Amtrak. The reason was not that of the CRI&P (couldn't afford it) or the Southern (which as I recall had its doubts as well as resources to continue passenger service), but I forget D&RGW's reason or at least the one I did read at the time (perhaps in Trains magazine or the Passenger Train Journal).
The GA situation was due to a tax break, and that "train" was a coach on an already-scheduled mixed freight for which "scheduled" was reportedly a generous term.