I don't have a definitive answer, but recently I was planning a trip to New York, and came across some incredible numbers. Both BoltBus and Amtrak depart from Baltimore Penn Station, and arrive at New York's Penn Station. (The bus stop is a few blocks away from each).
The Amtrak's high-speed Acela takes two hours, fifteen minutes, and costs at least $134.
The BoltBus takes three and a half hours, costing $15.
Both of these are demand-based prices, but the ratio remains effectively the same: for an extra hour of travel time, BoltBus is one-tenth the price of Amtrak. How is this possible?