Police and military do this specifically as a strategy at passive language. At least among those interested in linguistics, cops are famous for their usage of passive language to downplay violence they participate in: https://www.washingtonpost.com/news/the-watch/wp/2014/07/14/...

Basically, they do it because the terms are in some way dehumanizing.

I also find the terms dehumanizing, but specifically because I've noticed that it's most frequently a term used by incels, self-identified or otherwise. It's common on certain subreddits or on twitter to see users aligned in gamergate / manosphere circles using "females" when talking about women. And yes, these same people will say "men" when talking about men.

No they do it because it’s the correct term. If you say “a man wearing a white T-shirt” and the actual suspect is a 14 year old boy. Many of the people searching with disregard them in the search because they got told to look for a man. When it goes to court the defence lawyer would use it as doubt since the description is for a man and not a boy.

Police are also fond of saying "individual" instead of "person," which is another way of dehumanizing the people they encounter. It's always a red flag to me when I hear someone say the word "individual."

Dehumainzing others is one of the main characteristics of the military in wartime, and often the police in peacetime. You maybe have a pretty cool life experience not to have experienced that.

probably because they aren't