Stansted was developed for political reasons when BAA was Government-owned. It is simply in the wrong place. Its UK connections are poor, other than to NE London (not a prime travel destination).
It can only ever be an 'overspill' airport when other London area airports fill up. That is the reason it is emptying fast at present - Gatwick has become more customer-friendly. Luton is nearer to key markets (Central London and M1 corridor). London City has its own niche and Southend is competing on price, but also has faster turn-rounds and shorter flight times to most destinations. All offer a better customer experience to both passenger and airline than STN.
Undoubtedly STN will win some traffic back when the economy improves, but even then it will need to work hard to attract airlines to a remote airport dominated by the lowest-cost and most aggressive competitor.
Perhaps FR will buy it - that's the only way the airport will stay on good terms with its dominant client!