Parks does often give the impression that they’d rather the plebs didn’t actually go into their parks, but I think them booking ghost camps might be a step too far given they could just reduce the nominal capacity further to get the same effect.

I would bet the vast majority of the problem is your second option of people booking out campgrounds to avoid others (with a side helping of those who aren’t sure which day they want to go out so they book all options). Looking at who has a record of cancelling bookings would probably allow one to cut out a lot of this as I suspect you’d find a bunch of repeat offenders.