Nothing to do with the planes themselves. Basically Ryanair business practice forcing competitors to up their game resulted in an ultra-competitive slim margin industry.

On top of that many smaller cities actually paid airlines to fly to their muicipal airport. The idea that Brest would pay €2000 a day to fly 200 passengers from London to Brest, and those passengers would spend far more than €10 each in the local economy.

There's no particular reason they couldn't have paid for a subsidized train route to get the same volume of visitors.

Convenience? There's the Channel to cross so you have to go through Paris and Dover. A <1h flight becomes a 7+h train ride.

Of course, but that's just an argument for why planes will win, not why an airport-specific tourism subsidy helped planes win.

Lots of railway equipment (vehicles, signalling systems) is designed and manufactured in Europe, and obviously the construction and maintenance staff have to be, so I don't see why this decision would have been done for Airbus.

I think it's more likely to have been convenient for the politicians, who had incomes that fitted with taking weekend breaks to Paris or wherever, and good for their voters, on a holiday package to Greece.

Difference being that EADS is/was co-owned by different European governments and also serves defence purpose.

Further conjecture I heard that I'm repeating with no supporting evidence: it was partly a side effect the Cold War.

All the new airports built well outside cities meant that low cost airlines could offer flights to (near) a major city fairly cheaply, which in turn pulled down prices for the entire market.