Because the Commander in Chief is not under the Uniform Code of Military Justice - nor do we want him to be. I am a PROUD veteran, and I don't want my President to be under military jurisdiction. We have damn good reasons for having civilian control of the military.
While it does occasionally lead to issues like the one you noted, the alternative is unimaginably worse.
_I agree with you entirely regarding a civilian CIC. My question was more rhetorical. Society passes laws for both military and civilian government employees. The military standards are far more stringent than those for the CIC because society expects that anyone in that office would have the character to self-police. That expectation was shattered by the former RIMPOTUS.