I always thought it was because the fatigue monitor didn't measure rotational velocity, just +/-Gz (think I got that bit right!). Therefore any flicking led to an unquantifiable fatigue increase, particularly in the wing roots.
There probably isn't such a fatigue meter for light aircraft (at RAF budgets anyway), so it's all a bit academic.
We managed to break a wing spar doing the Cooper Trophy, must have been my slow roll recovery!