The idea is to emphasize the value of being active in the airline's FFP. Many travelers are cynical about seat availability in general for customers attempting to redeem miles. The idea is that the airline provides entire flights to popular holiday destinations, with seats limited just to members for award redemptions, to counteract that perception.

Even BA is only doing it with short-haul flights to destinations like Tenerife and Lanzarote which are heavily oriented towards leisure travel. They aren't doing it on routes aimed at business travelers, such as Heathrow to JFK. That would cut into their profits on key transatlantic routes.