They cost a hell of a lot of money to stage. Amongst other things, insurance is insane and exhibitors ain't cheap... even smaller jets like the F-86 and Hunter cost hundreds per hour in fuel alone. Military exhibitors, even foreign ones, can cost a lot less as their appearances are often a goodwill gesture, but there's no guarantee you can confirm them, and even if you do, they can often cancel for 'operational reasons'.
A good thing was kicking off with the Air Spectaculars at Baldonnel just over a decade or so ago, but after the last one was held some military operators filed complaints... their maintenance crews found crisp packets and other rubbish stuffed into air intakes after people wandered past the fencing unchecked.