City routes from marginal regionals just don't have the mass appeal or the required yield to generate a profit.
Surely that is exactly what Ryanair has done so successfully!
Airports do not exist just to serve the bucket and spade routes and not everyone wants to or should have to traipse through London if they want to fly to the major cities in Europe.
My point with NCL-BGY was that it was reasonably profitable and as far as I understand it, was discontinued because they wanted the plane to fly to Manchester. Ryanair was raining on Easyjets parade when they acquired GB Airways.