The track is mostly single track and heavily used by freight (where a few hours delay isn't the end of the world). Multi hour delays are extremely common and even with it being overnight, if you set off at say 11pm and aim to arrive at 8am, a 3 hour delay could see you arriving at 11am and your VIP passengers missing all their business meetings. They won't return!
FWIW I don't think Europe's push to overnight rail trains will be very effective either. It doesn't work well with overnight maintenance windows, and the yield per train is extremely low (100 passengers in 50 'rooms' vs 1000 normal seating passengers dictate a 10x ticket price). Also is extremely complex in Europe with many different signalling/communication systems, traction systems, etc.