Railway companies are national in nature and by history. The share of cross-border travelling is small; the income mainly comes from national rail.
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Obviously if they streamlined the process to take on airlines their revenue would increase. But perhaps the cost of streamlining would outweigh the revenue increase. Unfortunately it is almost impossible to create a disruptor in the train space due to rules, regulation and the capex nature of it. Whereas the airline space is easy to enter as a competitor even though it is capex heavy because the core asset (planes) are mobile. You can move them from very competitive market to another one that has less competition if the laws (and airport slots) allow for it.