With the movable curtain, I suppose you typically wouldn't have a lack of CDG-BER J availability mean no, say, IAD-CDG-BER J availability (unless there was enough Y already sold that you couldn't move the curtain back).

AFKL also probably has more of their short haul traffic connecting (especially from TATL) than LHG: being further west than LHG and having weaker alliance partners on the periphery force more connections through AMS and CDG (strategy differences between DL and UA (the latter being a lot more willing to fly thin TATL) also play a part). LHG may thus view short haul J as something they have to convince people to buy.