I forget what the normal ridership breakdown is between Chama and Antonito, Let's say it is 60:40. That's probably optimistic.
Let's make some assumptions:
1. Most C&TS riders are not railfans, and never heard of Chama before.
2. The scenary on the east side is just as good or better, than out of Chama
3. Antonito is more "on the way" to someplace than Chama.
4. There are rarely days the Antonito train is completely sold out.
So why don't we see a higher proportion of passengers out of Antonito ? I've always thought that some of the reason is that with the exception of the hour or so a day when the crew is preparing the train, the Antonito terminal doesn't look like an interesting place. Sure there's the fairly good looking depot, but everything else blends in pretty well with the rest of Antonito. Coversely, Joe Tourist could be drving into Chama and look down into the yard and think to himself "there's something interesting here". So they stop, maybe make arrangements to stay overnight, and ride the train next day.
Signs and tourist brochures are nice, but there's little in Antonito to give potential riders any hint of what they could experience if they take the time to ride the train. There's a bazillion tourists drving down 285 each day in the summer. If we could get just 5% to stop, maybe we'd be able to get another 5K riders without any additional cost.