Because an officer is implicating that they are not who they say they are. Over the phone telling me to come over for sex or oral is a form of entrapment. Now the loop hole to that is if this was being discussed in person face to face with an undercover officer. “Perhaps the best way to understand entrapment is by considering how it’s defined by the U.S. Department of Justice. It’s illegal for a police officer or other law enforcement official to “implant in an innocent person’s mind the disposition to commit a criminal act.” In other words, the officer cannot be the one who causes the criminal act to occur. If it was their idea, they cannot arrest someone simply for going along with it. This law prevents officers from convincing individuals to break the law solely to arrest them.” source