Interesting that there's even demand on those routes. I would imagine it's much cheaper by rail and similar time when you account for all the ancillary time wasters of air travel.
FWIW when I toured Europe as a young couple with 1 child back in the 90s, I wanted to take the TGV from Nice to Paris, but when we arrive at Nice on Thursday late afternoon, we were just too hungry to check out the train schedule first, so we did it after we ate. The last train for the day had already left, and IIRC it would have been a 6-8 hour ride (on Erev Shabbos) the next day. We headed to the airport and got a low fare (this was before ULCCs were around, so it was about $100 each, possibly less) first thing the next morning NCE-ORY. Was faster and cheaper IIRC.
Don't forget that train stations might also be not exactly where you need to go. It can easily be a 30-60 minute commute to/from the train station.