Cornwall has a population of just over 536,000 spread over 1400 Sq miles - it's just not enough people to support a public-service airport
There is enough people to support a public service airport, just not one the size of the real estate of St. Mawgan airfield.
Regardless of declared dimensions, at 300ft wide, there is more paved surface to NQY's runway than there is to any London airport runway, the place is enormous and it's never going to pay it way ... particularly whilst, quote, "very small town" Newquay actually has two commercial aerodromes.