The BAA spent far too much money developing an airport that is poorly sited in reference to the area it is supposed to serve (the South East and London).
They then spent even more money cajoling, bribing and pushing airlines to operate from there.
The result is an expensive white elephant unfairly subsidised by LHR and LGW. If STN had to stand on its own feet commercially, it would have to increase charges and its airlines and their passengers would flock back to Luton and Heathrow.
If the EU wants to investigate abuse of monopoly power it should start with BAA.