DSA is costly with it being a virtual base - crew are put up in hotels overnight. So that doesn't help.
But it probably all goes back to Easyjet's deal with DSA's sister airport at LPL. An agreement Easyjet probably don't want to be in, given their current 'keen-ess' on MAN. It was rumoured that DSA got a virtual base to avoid Easyjet having to put an extra aircraft into LPL that would then affect their growth potential at MAN.
Which is a shame for DSA to get caught up in this, since there is potential there for a based loco now TOM have gone back to just charters. While TOM are great for places like Greece, on routes like Malaga there is room for a low cost airline. And with Jet 2 and Ryanair both happy at LBA to the north and EMA to the south, Easyjet are probably DSA's best hope for large scale growth
Though of course lets not forget nothing has been confirmed about Easyjet's future at DSA yet