Sunset Limited has Los Anageles-Phoenix-Tucson-El Paso (Juarez)-San Antonio-Houston-New Orleans. Those are some pretty large markets !
It SHOULD have some markets, but...
(1) It doesn't stop in Phoenix. This kills the Phoenix market.
(2) LA-Tucson is a bit long for a corridor -- 10 hours -- though it would be fine if the train stopped in Phoenix, which it doesn't.
(3) There's nothin' much between Tucson and El Paso, and it's a bit over 5 hours travel.
(4) There's even more nothin' between El Paso and San Antonio (Del Rio metro area has a smaller population than the Fort Madison Iowa metro area, and the other two stops are hardly populated at all), and it's an even LONGER distance -- 12 hours travel
(5) The best population centers between El Paso and San Antonio are on the Mexican side of the border, and current immigration/border situation means that those people are simply not in the market for a US train. (If this were 1880, they probably would have been. But they're not an addressable market right now.)
(6) There are no stops between San Antonio and Houston, 6 hours.
(7) The small stops do NOT punch above their weight; unlike on the Empire Builder or the Southwest Chief where the smaller cities contribute disproportionately high ridership to the train, that's just not happening with Del Rio or Lordsburg.
This is not what corridors look like. Corridors have at least two big cities less than 6 hours apart, and a bunch of reasonable size cities with solid train patronage in between. There's a few reasonable sized cities between Chicago and KC; lots between Milwaukee and Chicago.
With a Phoenix stop, LA-Palm Springs-Phoenix-Tucson would be quite viable. LA-Palm Springs-Maricopa-Tucson, not so much.
If Phoenix service were restored, the problem section would be Tucson-Houston, with the El Paso - San Antonio part being the real killer.
The best idea I could come up with to improve the Sunset Limited was to reroute the Sunset Limited from El Paso to Dallas-Fort Worth via Odessa, Midland and Abilene, which would attract a *lot* more patronage IMO. If you could then continue to Houston via College Station, it would be even better.
San Antonio-El Paso is a bad passenger train route. It violates the "be on the way" rule of passenger train route design; it's 12 hours of nothing, and that's not what trains are good at. If we had free movement across the Mexican border, the route would look a lot better, but we don't. What trains are good at is stopping every hour or so to pick up and drop off passengers on a "string of pearls" route.
The only passenger train route in the US which has worse demographics than San Antonio-El Paso is the Alaska Railroad, but it's got far more tourism traffic thanks to Denali. It gets five times as many riders as the entire Sunset Limited route. Now, if the Sunset were daily, its ridership would probably triple, but still.
The Sunset East from New Orleans to Miami was a much better route than the current Sunset. :-(