I believe the way Easyjet works is the local base chiefs present proposals for new routes that they think will work, then upper management allocate aircraft to a base depending on the financial forecast they were presented with. So I don't think its really a case of the London office not understanding the Northern market, but more those on the ground being unable to present a plan that compares to those from other bases. Lets not forget Easyjet have bases all across Europe to think about - that's a lot of competition for the aircraft.
Also lets not forget that they both target slightly different market segments - Easyjet is more about city breaks and business travel, while Jet2 are more focused on package holidays and bucket and spade destinations. With the launch of Easyjet holidays recently, we may see a shift in focus in future, which Newcastle may well benefit from.