In the mid 70's -mid 80's Cardiff was Bristol the exact oposite position and it was very close to closing Bristol, with Cardiff pulling away into the distance. Its not the airport that needs Government money, it's the local businesses that need their help to reverse all the companies moving away to cheaper climes and locals becoming unemployed, which is why there is no passenger demand at Cardiff and airlines becoming uninterested in operating from there.
Get some jobs going in the area again and people back into work and eventually you'll see smilling faces with money to spend passing through doors once again to support an increase in the fortune of Cardiff.