Airlines will only move to other airports if the demand is there. They don't know the demand is there without intial expense of operating an initial start up route to gauge demand. That they dont want to do!
Ofcourse they can compare with operators that already operate or attempt some kind of survey but its not going to give the correct results. Regional Airports are vital to the growth of the aviation industry in the UK but its going to take more from the government, investors, consumers to actually help them develop.
If I had the option of Heathrow or Southampton for example I would take Heathrow any day of the week.