There's an op-ed piece by a ranking US military official called "Why Arabs Lose Wars" that touches on the phenomenon. Thinking back on it, there's probably more than a pinch of racism in its construction, but the gist of it is:

1. There is zero trust between enlisted and command. Officers treat their underlings with classist contempt, which is reciprocated.
2. There is no individual initiative, every order must come from the top, lest you be perceived as disloyal, or worse, competent. Which leads us to
3. Regimes are terribly paranoid of coups, so they deliberately hamstring their forces in organization, training, and equipment to hedge against it. Only the "Republican Guard" equivalent gets any sort of trust.