From information I have read from elsewhere one of the changes being negotiated is contract seasonality.
BA short haul at Gatwick is incredibly busy in the Summer season plus Christmas and New Year, less so November and February. Winter Sun and Winter Ski have in the past been useful at filling some of the gaps but not enough. For example Summer 2019 up to 90 daily departures, Winter 2019 45 to to 50 including the long haul. Although there may be scope for more winter destinations if costs allow.
It is similar for EasyJet who have about 30 to 40 seasonal destinations at Gatwick. I think they use those months to do a lot of aircraft maintenance too.