DND - LTN! Give us a break....
Luton is as far away from connections to central London as you could get as far as an airline passenger is concerned. It would be cheaper to travel to Edinburgh then fly to Heathrow or Gatwick and that has always been the case.
Or, alternatively, take the train.
Just because HIAL operate Dundee it doesn't mean that they can susbsidise the place in the same way that that the other "public service" airports in the group have to be.
Dundee doesn't come under that category and has to pay it's own way.