I think infrastructure plays a great role. An airport is expensive, but once you have it, you basically don't need infrastructure to link it to other airports.

I think infrastructure plays a great role. An airport is expensive, but once you have it, you basically don't need infrastructure to link it to other airports. (I guess there's a few beacons, lights and ATC centres, but compared to the price of thousands of kilometres of rail, this is nothing.) Compare to rail where you have to build and maintain all those kilometres that must cost a ton long term. From an article I read recently about trains in France, a high-speed rail line is in the €15B range on average. An airport is in the low billions (even Berlin new airport which is massively over budget is still only around 6B I think). Maintenance of a rail line is €300k/y/km from the same article, when maintenance for the (empty) Berlin airport was in the 20M range.