Stobart are concentrating on achieving their 2.5 mppa target for SEN and see a MAN route as producing far greater numbers than GRQ or CFR ever will.
That's a pretty naive mentality, it reminds me of Airtours vs Thomson, Airtours were selling more holidays but their 'quantity' never did manage to outdo Thomson's 'quality'.
If there is water to cross the air fare is higher, to/from Manchester, that's Manchester rather than the airport, one needs to compete with the trains, National Express and driving and by the time London folk may have made it to SEN in time for their 45 minute check-in, or whatever, they could have already been halfway to Manchester by surface transport.
Stick with crossing water Stobart