Plane only seems cheaper in many cases. Shuttle to and from the airport can be as expensive or even more expensive than that flight. Frequent delays / cancelled flights, check in misery, security theater and so on. If possible and available I'm more than happy to take the Thalys, ICE or TGV.
What really made the difference for me is that the 4-5 hour train ride is done after 4 to 5 hours. My 1 hour flight starts 3 to 3.5h before the flight to get to the airport and through security and at the destination, after de-boarding, I'll spend another hour for security and to get from the airport to my actual destination.