They have jobs because their recruiters have assembled a good team for them to waste time with. I was at a high-level military job a few years ago, and the question arose: why should these people pay any attention to a gym owner when a D1 strength and conditioning coach was telling them they needed to do circuits on Hammer Strength machines? I told them that a D1 S&C coach works with a demographic that is hand-selected for genetic freakiness. When your entire professional career has been spent with athletes who walk into your building with a 34" vertical, <4.6 40yd time, and 225 x 15 bench press strength, you might well be of the opinion that machine-based circuit training is the way to go. After all, look how well the kids are playing! If the only people you work with are freaks, ANY S&C METHOD LOOKS LIKE IT WORKS. And if you follow the progress of kids on this shitty program for 2-4 years -- that is, they don't make any progress, but they don't really peter out either unless they get injured -- you might well be completely ignorant of the training advancement curve described in PPST.
On the other hand, if you work with the general public in a situation where you get paid if you keep people interested because they are getting long-term results, and you watch what happens when you take rank novices and make them into advanced lifters over a period of 1-15 years, you might learn a few things about stress/recovery/adaptation. Especially if you're training yourself and are personally interested. And most especially if you are unencumbered by the dogma of swiss ball and core stability/Matveyev's undulating periodization model for everybody/hypertrophy only happens after the first 6 months/10-12 exercises using 8-12 reps for 4-5 sets at moderate intensity, or one set to failure is enough/full squats are bad for the knees/deadlifts will shear the spine/presses destroy the shoulders/Olympic lifts cannot be taught to everybody/more exercises is better than heavier weight/power comes from plyometrics, not strength combined with genetics/everyone on the team can and MUST do the same program, because we're a Team/etc., etc., ad nauseum.
So the simplest explanation is that when your job description doesn't demand it, when your tenure-track professors don't teach it, and when you aren't in a position to learn it, you won't know any better. Depending on the athletes, or in this case the soldiers you work with, this ignorance could be expensive. He seemed to understand.