A 5x disparity is still a lot more than a 2x disparity. In fact, considerably less than 2x given the overhead time of traveling to the airport, security, boarding, etc.
How many people would pay 8x the ticket price for a 45 minute flight from Paris to Munich (The Concorde was ~8x the ticket price of economy subsonic flight tickets)?
There are. A flight is about an hour and a half, a train is about 5 hours. Far more people fly between the two every day than take a train.