Yorkshire actually generated 9.4 million passengers in most recent available statistics. Scotland was double that, the North West was 15 million. There are 3 airports in Yorkshire and Humberside, not 4. Nobody is going to build a wall around Yorkshire, so nobody is going to stop the flow of passengers to airports just outside of the boundary (or to London airports, for that matter). So your argument is fundamentally flawed.
Just to quote some propensity to fly (per person) statistics;
London 2.94
Scotland 1.72
South East 1.44
North West 1.01
Eastern England 0.96
East Midlands 0.76
West Midlands 0.75
South West 0.73
Yorkshire and Humber 0.72
Are you going to go off and argue with yourself on your fantasy thread now LA?