They do all the time. Ego's. It depends on the jurisdiction too. Sheriffs, in small towns are voted in, so they're more accountable to the people. In big cities you get lost in the crowds, there's just so many people that its almost impossible to maintain order in an overall sense. Naturally the imbalance of power is larger in big cities, so cops take a different role. In such a situation top down authority is the only thing that works, the boots on the ground understand this, and it goes all the way up the chain of command. If the State government is on the local level's side then they can make things very difficult for the feds. The feds however are the central authority, so they kind of have the final say. It's like your childhood friend, you'll put up with him being a cunt cause he lets you ride his jet-ski.