Continuity mistake: Ruzek and Hailey are waiting to swap cash for guns. The pickup truck drives up very close to them and stops but then when the driver exits the truck he is parked a considerable distance away.
Center Mass - S7-E14
Continuity mistake: While Rojas and Upton are questioning their suspect in the interrogation room, the plate with a sandwich is constantly shifting position from near the detectives to immediately in front of the suspect with no-one touching it.
Center Mass - S7-E14
Continuity mistake: Atwater and Rojas begin to chase a suspect out of the library where he had been spotted by a uniformed officer. As the chase begins Atwater moves ahead of Rojas with the officer in a distant third place. As they emerge from the rear door Rojas exits first, followed by the officer with Atwater behind him by several seconds.
Character mistake: When Ruzek and Voight are questioning Wade Henslow (the father of missing girl) at the station, after finding out he lied and set up his own security to find his daughter Adam looks at Wade Henson but addresses him as "Mr. Larson" which is actually the last name of one of the kidnappers they found DOA who got into the gun fight with his security guy, the ex-cop Kenny. (00:21:26)
Answer: Because he is a great cop and gets the job done better than anyone.