I don't think it's reasonable for airlines to expect to maintain the same number of departures that worked in the nice summer months through the winter. Runways will need to be cleared, planes will need to be de-iced.
They could keep extra planes and staff around ready to replace an incoming flight if it's delayed (clearly easier for carriers with fewer types of aircraft). Heck just staff seem like they would be handy as the flight crew hit their service limits.
But there's no financial incentive to do that if "weather" (despite happening every winter) is a get-out-of-jail-free card.