Why do police constantly break the law by violating people's Constitutional rights?

"In a scathing report, the U. S. Justice Department said Orange County prosecutors and sheriffs ran a jailhouse informant program from 2007 to 2016 that violated the rights of criminal defendants. Using informants is not prohibited, but Orange County authorities made them "agents of law enforcement" who elicited information from defendants who were represented by lawyers, a violation of the 6th Amendment. Convictions for murder were set aside because of the scandal."

Why do police constantly break the law by violating people's Constitutional rights?
Post Opinion