I may be wrong but with the exception of the JFK based cabin crew, having an airline operating on a French AOC, with a French base and inevitably a number of French employees means a company having to pay French social taxes, which isn’t cheap at all.
Actually, the above is a quote of my own post on the OS thread in R&N. Could someone please confirm or deny this? I'm under the impression that Easyjet pulled their Paris base a couple of years ago as they would be held liable to pay French social taxes.