IIRC the bigger component was the time issue. When the flight is an hour and the train ride is 3 hours it makes a big difference. But I would imagine it's seat

IIRC the bigger component was the time issue. When the flight is an hour and the train ride is 3 hours it makes a big difference. But I would imagine it's seat density (more seats in a plane fuselage vs a train car) and sold seats vs empty seats (airlines have a pretty efficient system for filling seats based on dynamic pricing, due to the fact that the flight departures are timed and gated). I'll try to find the article, it had numbers.