I forget where I read it, but someone hit the nail square on the head -- in wartime, you wind up promoting those who have shown the ability to get the job done under fire, in peacetime, those promotions go to the more typical managerial types.
The top brass (and the civilian overseers) want the military to run like an accountant's office.
Well, that's logical, isn't it? You can never know who will respond under fire and who will fold until they've actually been in that situation. We had a PL in my Company who was a royal screw-up in just about any/every situation, but when the shooting started, even I had to admit, he kept his cool and worked the situation. Then there was a guy in a different Company, big, bad, tough guy, Ranger, loud, etc. who was relieved for cowardice (deservedly so).
You just never know.
In peacetime “paper bullets” are as deadly to officers and senior NCO’s as real bullets in wartime. Usually the paper-variety kills the warriors who would otherwise be your leaders.