There is a world of difference between a display and a flypast. Both require high level approval and supervision but a flypast does not take anywhere near as much practice.
Planning for a large flypast may take several weeks but it will usually only entail one or two airborne practices.
I can assure you this is not a case of ‘Parkinson’s Law’. Getting a display right takes practice. I have plenty of Hawk experience but I wouldn’t fly a low level display without a lot of practice. It’s a confidence thing as well as a safety thing.
I have flown many loops in a Hawk. Never below 5000’ feet though. To have the confidence to pull through when the ground looms large in the roof would take some convincing.
BV