Big population
Big population=big airport. Yes, but the airport isn't necessarily right next to the big population. For example Rotterdam/Den Haag/Utrecht in the Netherlands - a sizeable population and much industry. Rotterdam has a small airport for local needs, the main airport being Amsterdam Schipol.
This works fine with fast road and rail connections.
Leeds/Bradford/West Yorks has a local airport with better services than Rotterdam. The main airport is Manchester which has good and improving road and rail links. No need spending more money at Church Fenton to provide something which is already available. Can you honestly expect CF to have anything like the range of flights MAN has. Ever?