A lot longer. There's at least a 5x difference between typical plane and train speeds. So a 5-6 hour flight becomes a 25-30 hour train ride. That's a pretty major cost and inconvenience you so blithely dismiss as long as it only affects someone else. Also, please note that it's not that uncommon any more for people to travel over water, and there are no trains there. But I suppose you'd say those people who aren't you should just constrain their choice of job or occupation accordingly.

Nothing's a big deal when it's somebody else's problem, right?