I have to agree with EI-BUD. LGW was/is a decent choice.
London is, by most population metrics, the largest city in Europe. That offers a pretty attractive catchment area for an airline with the right offering. So, if you're a manager of EI, with a foothold at LHR, how do you expand? LHR slots are expensive, STN is FR central, similarly LTN with U2 and LCY is limited with the aircraft it can accept ... by a process of elimination LGW is the only option if you want to increase your slice of the London pie.
Of course, the other elements of the equation are the right product at the right price and the right economic circumstances, but just because FR or U2 are operating in the neighbourhood is no reason to not attempt to make a pitch.
JAS