Because they have different priorities than you do.
Humans, like most everything else in the universe, seek to maintain a sense of equilibrium in things. This is true for not just matters of physiology, but for social interactions as well. Think about the interactions you have on a daily basis: In most all of them, you enter an interaction with at least a neutral mindset and perhaps even an assumption of goodwill. When a guy wakes up next to his partner, he doesn’t harbor an innate suspicion about the partner’s motives—he assumes that the partner is as goodwilled as she was when she fell asleep, and the couple’s interactions proceed on this assumption.
Or think about your interactions at work. Absent narcissism or self-deprecation, when you go into a job, you default to considering your peers as more or less equal. Of course, as time wears on, you begin to categorize people, but those initial interactions will be civil and respectful, because that’s what’s expected—that is the silent understanding wrought by the norms of your workplace.
Now, think about the workday of a police officer. Her job assignments consist, primarily, of being dispatched to successive 911 calls. When someone calls 911 for police service, there is a tacit admission by the caller that the situation at hand has deteriorated beyond the caller’s control and police are needed in order to bring the situation back under control. That is the unstated assumption that the officer has going into each situation—not that a social equilibrium needs to be maintained, but that a situation needs to be quickly and efficiently brought back under control.
Further than this, when she gets to the scene of many to most of these 911 calls, she encounters people who seek to frustrate her endeavors. She talks to witnesses who lie in circles about not seeing anything. She talks to suspects who lie about where they’d just been or what they were just doing. She talks to drunk people who can’t coordinate themselves and won’t remember what she said in 10 minutes. She talks to addicts who try to conceal the fact that they’re high even though involuntary tics have consumed their body. She talks to grade school kids and teenagers who have been conditioned to mistrust or despise police. She talks to people who lie about their identity because they have warrants or because they just want to frustrate her. She talks to people who act nervous and take too long to answer simple questions, raising her suspicions. She talks to people who have drugs, guns, knives, and any manner of other contraband hidden in their residence, in their vehicle, or on their person.
Now consider that the officer is doing this many times per shift—10, 20, maybe more—encounters every day. She will quickly learn that, in order to get anything accomplished with these liars and obstructionists, she is going to have to employ tactics that in any other field would be unacceptable. She is going to have to be blunt, brusque, and curt. She’s going to have to call bluffs and smokescreens and BS. She’s going to have to interrupt rambling, circular explanations. She’s going to have to look people in the eye and say, “We both know that you’re lying to me right now.”
And through it all, she will begin to develop the opposite assumption from the freshly roused partner and the guy at the water cooler—work interactions are not among peers, and people are likely not worthy of implicit trust.
Now, you, who I will assume is a normal, everyday citizen, comes into contact with this police officer. Even though she can probably surmise that you’re not a frequent flyer, she doesn’t know you and doesn’t enter into interpersonal contact with the same assumptions you do. Additionally, if she’s in uniform, it’s possible she has a task at hand she’s focused on. Until you are a known quantity, you may be treated coolly and humorlessly.
Now, let’s take a step back. You, the partner and/or co-worker, interprets the response of this police officer through the lens of your expectations and judge her to be arrogant. I mean, after all, she’s acting all distant and aloof and snobby, right? However, your assessment is based on your interaction in a vacuum and likely doesn’t factor in much of anything I just said. That doesn’t mean either one of you is “wrong.” You’re coming from different places.
In closing, I’d bid you to be forgiving. This officer cannot afford to give people the benefit of the doubt, because there are only so many people you can relax your guard around in her line of work before she gets herself or someone else hurt or killed. Be gracious to her, for her burden is great.
This man beside us also has a hard fight with an unfavouring world, with strong temptations, with doubts and fears, with wounds of the past which have skinned over, but which smart when they are touched. It is a fact, however surprising. And when this occurs to us we are moved to deal kindly with him, to bid him be of good cheer, to let him understand that we are also fighting a battle; we are bound not to irritate him, nor press hardly upon him nor help his lower self. —John Watson, c. 1903