Some people just don't like flying. Some dislike all the hassles of security, luggage allowances, restrictions on liquids and all of that stuff. Some just like trains!
Speed isn't everything to everyone. There's also comfort, convenience and enjoyment to think about. Still, I'd think that most travellers fly, but not all of them.
I went to Berlin for the day yesterday. 5am pick up in a taxi to Gatwick (from Hatfield), arrived 6.20am - flight 8.40am. The company that booked my taxi had to book me that early for insurance purposes, so I wasted loads of time at the airport.
Two hour flight, then 30 minutes from airport into town.
Back, same thing with an early taxi, to an airport with very little to do and a delayed flight (by the end of the day, easyJet had been losing time on each flight).
Back to Gatwick at 11pm, had to wait for taxi driver, then back at 1.30am.
Obviously a train to Berlin would take a long time, but given the fact I could start from St Pancras (25 minutes journey for me) and not necessarily need to get there anywhere near as early, the extra time for train wouldn't be as excessive as many would think (comparing flight vs train times directly).
I really do hope we might get trains to Cologne one day, as I'd quite like to use the train instead of flying - especially for leisure trips.