DAZ211
Check your map mate - last time I looked LHR was directly west of London, not south of it.
Leisure traffic - the traffic you interviewed on your last flight - is not the traffic that keeps transatlantic airlines in business.
Plus, where people live is not the major factor for airport choice, a bigger influence is where businesses are located.
Airport and business location for decades have gone hand in hand - hence why the west of London and the M4 area around Maidenhead, Reading etc where the UK offices of numerous multinational corporations are located.
Just as you express frustration at driving to Heathrow - likewise inbound business passengers would be frustrated at arriving in to STN and then driving past LHR to get to their company's UK office.
Foreign airlines will ALWAYS want LHR first, if that is not possible they settle with LGW.
The only way for STN to see big expansion other than from FR or EZY is if the (virtually) impossible happens.
1 - BA move in (like they did at LCY)
or
2 - an entire alliance ups sticks and moves to STN - say all the Star Alliance carriers move together.
If either of the above ever happens I will eat my own hair.