You get curt answers, or no answer, or sometimes deliberately rude answers. This is not true of all cops, but it's true of enough that people can get tired of it. So you stop talking to them, which makes them feel disliked, which makes them more distant. Yet the same cops, if you rode with them, would be considerate and friendly. Cops talk about how much they value support from the public.
White males seem to default to all-business, to distant authority.
While female cops can be disagreeable, on average they are better with people. Whites often seem to be almost hiding behind a shield of officiousness to avoid personal contact with the public. Some of the stiffness I think comes from the nature of a cop's dealings with the public, which usually aren't happy. Officers constantly tell people to stop doing things, arrest them, give them tickets. It's hard to be warm and fuzzy with people who are angry at having been stopped, who resent authority as almost all of us seem do, who are trying to find excuses or claim innocence.