I'm convinced that AF's failure to get BRS-CDG to be sustainable is because of their unrealistic fare rules ex-regional airports. If you want to do less than two nights (or a Saturday) away, the fares can be eye-popping.
EZY are able to demand good fares because they're also offering flexibility. It's easier to pay EZY £320 for a one day return than it is to pay AF £550.
Another miscreant on that front is SN to BRU. Talking to a colleague who had to take a one-way BRU-BRS (followed by BRS-DUB on EI, and DUB-BRU on EI), he paid €350 one-way. (He should have bought a return spanning a weekend for €250 and binned the return leg).