I don't understand what you don't understand.
If the critique that was posted was noteworthy, then that means that such a critique isn't standard.
@Autothrust Blue's description makes it sound as if such critiques were not a regular part of his operational flying experience, and that the critique was warranted. Since bad habits and techniques don't just randomly pop out of the woodwork one day, there was probably a trend of whatever those techniques were that existed before the pointed critique on that one day.
I grew up in a professional environment where critiques like that weren't just standard on every flight, they were expected and solicited if they were not given thoroughly enough. In that environment, perfection was the standard. Since the perfect flight hasn't been flown since the beginning of flight, that meant there was always something to debrief, to learn, and to improve on. Every flight, every day, egoes are left at the door and honest critiques are given and received in the name of striving for that goal of perfection.
For some reason in the civilian flying world (and I've seen this in many different corners), pilots aren't able to give and receive performance criticism regularly and understand the difference between
personal and
professional. Far too many folks mix the two, and cannot handle honest assessment and critique of their professional performance and separate that from it being a critique of them as an individual or as a pilot in general. This leads to butthurtedness (the technical term) on the part of the receiver, and leads to tentativeness to give critiques on the part of the giver...and ultimately at the end of the flight, it can lead to two guys shrugging their shoulders when the word "debrief" comes up, and the answer is "I've got nothin'".