Ignoring the horrendous M62 West, the hour journey crossing Leeds to LBA and the increasingly unpredictable M1 South to EMA for anyone South/South East of Leeds, there is a large bucket & spade population East of the A1 & as far South as Peterborough & North to York for whom DSA is the preferred airport.
If DSA is the preferred choice for all those you mention above,why is the number of passengers using the airport decreasing year on year? If what you say is true then airlines would be falling over themselves to provide routes to service the demand.