It's worth remembering that in the late 1990s Stansted was very much underused and perceived as an airport with very few passengers. I really don't want to get into the BAA cross subsidy / merits of LCC issues but STN has now become accepted as an airport people in London will actively consider for leisure. Took many years for STN to migrate in public perception from empty shell to busy. It will likely take SEN a long time to gain public acceptance from people in London rather than just Essex.