I take it you aren’t a CFI, based on that response. Yes, there are CFIs out there who speed through the ratings and manage to find lenient DPEs, but that’s true for pilots of all ratings.
There are some circumstances where if the CFI is a little less attentive than they should be (and sometimes the difference between “attentive enough” and “not attentive enough” is on the order of seconds), the situation can quickly devolve into one where there isn’t enough time to react.
Add in the pressure of having the student and parent on board and it’s understandable how it’s possible the instructor may have overlooked some preflight planning and let the situation go just a little too far before there was adequate time to correct. It also could have just been a “simple” case of poor airmanship, but again, this affects all pilots.