Some ticket prices are crazy, but the issue is a lot of trains are already very busy especially at the weekends, even with those prices.

If trains were made cheaper, some of them would become extremely unpleasant to use. In an ideal world, we'd have both more capacity on the busy routes and cheaper tickets, but that will need a lot more work than just nationalising the train companies.

(Or just fewer people would solve all these problems, but that doesn't look likely to happen...)