I suppose it all boils down to the fact airlines (not necessarily passengers I hasten to add) want LHR and LGW. When they can get the slots, they'll move in a heartbeat.
Whilst STN has had some success with the likes of EK, Jet2 and the odd other interesting carrier, it too frankly struggles to attract, or at least retain, a diversity of carriers. MAG continues to bang the drum on long-haul potential, at least before the pandemic, and largely on the basis of lack of capacity in LGW and LHR.
In all honesty, if many airlines won't settle for STN, then LTN is only going to find it even harder. The only exceptions really are the likes of EL AL and Blue Air where LTN has a clear advantage to serving their demographic.
Passengers on the other hand, I believe, would travel in similar numbers to other airports besides LHR and LGW if that's where the flights operated. It's a requirement far more for airlines rather than passenger preferences in my view, who always seem to have this image that LHR is just off Trafalgar Square and STN or LTN conversely are in the middle of the outback.
Unless there's a clear alliance partnership for hub connections, or Virgin/Delta type interlining agreement (which admittedly is most cases) there's little reason really to serve LHR over the other London airports other than national pride or perception alone and not really within the passenger's main interest, which is a shame.
Last edited by FRatSTN; 18th Jun 2020 at 16:03.