Starting when he comes on the force as hardly more than a kid, a cop can tell people what to do. He can make U-turns that others can't, stop traffic, give tickets, arrest people. He carries a gun, often concealed when off duty. People thirty years his senior have to do what he says. And in his adult life he has never known anything else.
Most cops handle it reasonably well.
The ones who don't are hard to take. They're the ones everybody remembers. Finally, there is the need to maintain authority. If you are chatty and buddy-buddy with people, they will use it against you. How about letting me slide on running over these kids or having twelve kilos of marijuana for personal use.