Southend drove volume deals with both easyJet and Ryanair which drove short term unsustainable throughput. When the intro deal runs out, the locos relocate the fleet to somewhere with a better deal, SEN never managed to lock them in with a deal that the airport would do well out of. Again, if Southend stopped all passenger ops tomorrow, the totality of the operation would easily be handled by Stansted and others. Like Manston before it, it adds nothing that's net new, it really just cannibalises competitors.
But I know what you mean, it's a crying shame, very painful for local jobs and businesses. Very sad.