I once had a conversation with an Amtrak Marketing guy who was trying to figure out how to implement a service using the Southwest Chief. This guy was traveling in my sleeper, and the trip was light enough that we had time to talk. We agreed that it would be impractical to expect people to drive into the heart of Chicago for the service. A loading location like Joliet made more sense. It should be someplace accessible to the Interstates.
The tentative plan called for the auto carriers to be dropped in Flagstaff. If they had been taken all the way to L.A., that would have seriously limited the destination options. By dropping the carriers in Flagstaff, travelers would have fairly direct access to the Grand Canyon, Las Vegas, Phoenix, or Tucson. Flagstaff would also be a reasonable starting point for California destinations.
But look at the schedule: Arrival in Flagstaff is in the evening; later if the train is delayed. The ideal is for people to wake up after a night sleeping on the train, then get in their cars and drive in daylight. This schedule means people would arrive in Flagstaff just in time to find a motel and sleep. I don't know the situation now, but Flagstaff had barely enough motel rooms then. They would have been in short supply for additional travelers from the train.
It was suggested that the auto carriers could continue down the Peavine to Phoenix on a new connecting train. This would allow for a morning arrival, but would mean the expense and equipment needed to instate a new train on that route. Would Santa Fe (now BNSF) cooperate? Travelers for the Grand Canyon or Las Vegas would be taken farther from their destination. Travelers who want to drive to Southern California would not benefit at all in terms of mileage; in fact, they would have to pay extra for the additional rail mileage.
Traveling in the eastbound direction would entail similar problems.
As I said, the current Auto Train represents a perfect storm of route, distance, scheduling, cost, geography, and demographics. You'll have a hard time finding a route that has similar characteristics ---- anywhere, ever.
Tom