I think it’s more nefarious than that. Many departments want a good 'ol boys club where they’re the ultimate authority and they want their officers to fall in line rather than question department actions.

This internet myth has got to die. ONE case in ONE department, a quarter century ago, does not mean it’s a practice.

https://www.nytimes.com/1999/09/09/nyregion/metro-news-briefs-connecticut-judge-rules-that-police-can-bar-high-iq-scores.html