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

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.