In Sweden a flight from the northern parts to the southern is about $100 and takes an hour. The train cost $100-200 and takes about 16h depending on where you depart from.
I believe a requirement for people choosing to take the train is that they add some facilities (you feel pretty nasty after 16h on a train) and reduce the price. Raising the price on flights won’t help unless it’s drastically, around 2-300%. And if you do this on domestic flights then nobody will afford international flights.