Air Moldova used to fly to Stansted when they first went to London then they transferred to Gatwick, I assume that they are coming back because of the fees at Gatwick. Adria also left Gatwick for Luton before quitting the UK altogether. the Tarom service goes back to the day when the government dictated which airport an airline would serve in London and Eastern Europe was allocated Stansted. Tarom stayed after everyone else went back to Heathrow if I recall correctly.
If its all about fees them maybe Flybe can be persuaded to move as they have taken GAL to court and lost on the Gatwick pricing policy.