Perhaps out of topic but to answer Akrapovic in his specific detailed description of loss of control accident caught on camera, I would think in this particular scenario, there is a precise answer as "As to why", and this is wrong imputs to correct an overbank with nose dropping, whatever the cause of that overbank..
This is due to lack of specific training from flight instructors, whom are certainly fully qualified for normal operations have often no clue of how to recover from a degrading unusual attitude situation, such as this one. They applied the wrong inputs relying on deadly intuitive inappropriate instincs trying to raise the falling wing with opposite aileron and pulled on the elevator at the sight of approaching ground.
One should view slow flight below the second regime / stall / spin as another flight regime with its own rules and techniques, one can easily make an analogy with driving on snow and ice which likewise has its own rules and techniques, both anti instinctive as in the former LOC flying scenario.
When loss of control happens while driving on dry pavement with a contemporary vehicle ( Old rear wheel drive vehicles without computerised electronic stability assistance are different ) the reflex is to release the throttle pedal and hit the brakes, which is essentially correct. But in icy slippery conditions the worse thing to do is to reduce throttle pedal and hit the brakes.
Likewise during a stall / incipient spin scenario like the one above, the worse reaction is to apply opposite aileron- in a situation of aileron reversal- to lift a dropping wing and pull on the stick leading to a flick. Whether the situation was recoverable or not due to suficient height I don't know, but control inputs were utterly wrong.
Unless they had some technical or other issues leading to the upset, what was lacking for a safe outcome was early recognition of the degrading situation followed by wrong recovery inputs when it was already too late. However typical 1000 ft agl height in the traffic pattern allows for immediate recovery like in 1/8th of a turn if the correct reflexes and appropriate inputs are applied.
Like taking a course and practicing active skid / brake / throttle control on an snowy track with your vehicle, indulging in uprt-loc advanced aircraft control training saves lives.
As far as the Pitts accident at White Waltham is concerned, instructor was duly qûalified and used to those maneuvers, I would rule out loss on control..Something else must have happened RIP