But doctors do not end up "aware of their impaired decision making abilities when tired" after that grueling period. They emerge convinced that they are used to being tired, able to work long hours and generally an exception to the "decision making abilities are impaired" thing.

The situation is normalized in their heads, they lived it so long that they see it as normal.

And with military recruits, they are made to sleep a little so that they are easier to coerce and mold. Then not being able to think is a feature.