Many police forces conduct a form of intelligence testing as part of the hiring process. If you are too intelligent then you will be booted because they think that police work will be too boring for you and you'll quit. The police departments across the land provide much of the "talent" pool for the FBI, DOJ, DEA and other three letter agencies which naturally leads to the three letter agencies brimming with fools.
It would be more accurate to say that you read about the New London, Connecticut police department and extrapolated from that one case to "many".
In truth, I had heard of this from HR personnel and officers in the LAPD, Sacramento and Seattle PD as well as from corrections departments as far back as the early 90s when I applied. Additionally, the written tests included very obvious personality and IQ testing. The New London case merely brought it out in the public light.
If you can't learn to do it well, learn to enjoy doing it badly.