If you were a student and had a choice of 2 brand new instructors with minimum hours would you want the one with CPL knowledge or the one with PPL knowledge?
I don't think that will be (always) the issue. More likely scenario is to choose between a 1000s hours/many years PPL instructor and minimum hours/years CPL instructor - who would you go for?
From the theory perspective - which the question is about - flame-out of a jet engine or ATPL license hour requirements, while maybe of interest, are of no help in training a better PPL pilot - I suspect they are only patience tests (making maybe sense for ATPL level but of doubtful value for instruction in PPL training) - this just shows that all flight training/licensing is set up for ATPL and anything around it is just droppings from the table and that's why there is a CPL theory requirements for instructors (some requirements must be made and this is the one closest... I guess was the thinking)