One major issue is that there are few LD routes and so your desired destination might not be accessible by Amtrak without traveling to the closest possible station and then renting a car for the remaining distance. Or getting to your desired destination might require multiple trains necessitating layovers in cities other than your final destination. But if it's a straight shot on the train, I suspect it's only more cost-effective to take the train on trips over 1,000 miles. Still, driving is very stressful for me and the scenery is generally just ugly freeway, whereas I enjoy the time on the train and depending on the route, the scenery can be fantastic.