It's worth mentioning that more than half the traffic on nearly every long-distance route comes from people traveling less than 500 miles:
88.1% Palmetto
77.3% Cardinal
71.0% Texas Eagle
69.1% Silver Star
66.3% City of New Orleans
65.1% Coastal Starlight
65.1% Crescent
62.6% Lakeshore Limited
62.3% Capitol Limited
59.9% full long-distance system average
55.3% Empire Builder
53.5% Silver Meteor
53.0% California Zephyr
50.2% Sunset Limited*
43.9% Southwest Chief**
*Includes Los Angeles-Tucson, at 502 miles, Sunset Limited's busiest city pair
**Southwest Chief has 52% of passengers traveling under 600 miles
Here's where these stats are coming from
https://www.railpassengers.org/resources/ridership-statistics/
Of course longer segments generate more revenue per passenger. One coach CZ passenger Chicago-Omaha is as low as $63, one coach CZ passenger Chicago-SF Bay is as low as $141. And rooms (which are much more revenue) skew long haul, of course. But the majority of passengers and a very significant portion of revenue comes from people do much shorter trips.
Trips in the under-500 mile range are far more competing with cars than planes. Many popular segments are 4-8 hours drive and the train is often pretty competitive timewise, especially when one considers people likely made a stop on such car trips. in some markets planes are definitely a competitor, but in city pairs like this cars tend to dominate over flying regardless of the presence of Amtrak. Many city pairs such as Memphis-New Orleans require a connection which kills the time advantage. And even for markets which do have nonstop flights they are often the hub-feeding short haul flights with high air fares such as Minneapolis-Grand Forks, Atlanta-Greensboro, etc.
For people traveling these sorts of city pairs on long-distance routes the choice of train is not the huge time penalty, the sort of "who choses to take a two-day train when they can fly in hour hours?" sort of proposition. In these shorter trips the question tends to be why do people chose the train versus a car. And that tends to be categories like these, some of which have been mentioned before:
--People without ready access to a car for the trip (zero-car and single-car homes by choice or financial constraints, students)
--People who do not drive (young, old, low vision & health issues, the choice not to learn to drive)
--People who don't wish to deal with the traffic, bad weather road conditions, etc.
--People who want to avoid the unproductivity and fatigue of driving
--People traveling somewhere that a car is unnecessary or even a liability (visiting family/friends who will drive them around, people visiting a big city where a car is not needed and parking is costly)
Most long distance trains have fewer than 10% of total traffic being people who travel from end to end. Certainly it's more than 10% of revenue, again, because the longer distance passengers pay higher actual fares (lower cents
per mile but raw fares are higher) and they are more likely to occupy expensive rooms. But the LD trains serve far more people traveling far shorter lengths.