BUT, the greatest majority of people paying their own ticket want the lowest price and the carriers will show them the lowest price to get their attention.
That's not true ... One want's the most cost effective and convenient trip and 'cost effective' includes travelling to/from airport of departure, transport costs, car parking, buggeration factor etc. etc. etc.
Now, let me think when I lived in the East Midlands, probably 1.5 hours from LHR, my regular destinations included AMS, CDG, DUS, FRA, MUC, CPH, ARN, MXP, FCO, RIX, KBP, SIN & HKG and, amazingly, I could achieve all of these, regularly, at schedules that suited my purpose, and at trip prices that suited my pocket, from BHX!
Now how many imagine that one needs to travel to London, perhaps Manchester, to travel to these destinations? ... It's a case of educating the travelling public, many will be driving past such an airport as BHX on their way to/from London, spending perhaps hundreds in travelling costs to save a tenner on an air far?