Usually they are the people with no talent or ability to get the job done.
Why do some people feel that they have to "brown nose" and "back stab" others in order to get ahead in life?
Because it's easier. It's too hard to get credit for doing your own work, and people find it complimentary when others pay attention to them, and kiss their rear end. People like that are wired differently, they usually come from anything goes, win at all costs environments. They have no scruples and will level anyone who gets in their way.
I stay away from people like that at all costs. At my last job, my biggest deciding factor for leaving involved a rear end kisser who was running amok and wrecking a lot of havoc. It was very disruptive. Unfortunately they are everywhere. I always ignored their existence. Maybe that was why I was targeted.
It's hard to say why people (in general) behave any particular way or what their motives are .. This type of behavior may simply suggest a person's priorities.
The people who tend to do this are either lazy, jealous, insecure, or have no ability of their own to shine a light on. The best thing to do is not let them get to you. Karma usually comes along and bites these people so just sit back and bide your time. It is usually well worth the wait.
The unfortunate truth is that for some, that is the only way to get ahead in life.
Lack of ability, lack of integrity, lack of moral standards -- so they crawl up the ladder by whatever means they can find. Such people may be contemptible but their name is legion.
It's a business of weak people.
People empty of personality, without plan, without self structure, without self respect, without strength,
Despite almost everyone saying about "not having an ability' well, everyone has an ability, a talent, but the point about these kind of people is that they are lazy enough to reach their own talent. They don't bother about focusing on their own lives, it takes too much time and effort to take the best out of the self and build yourself and the path ahead, but back stabbing ? It's easier to shoot, for some it's more fun!!!
Each human needs a code in life, these people doesn't have one.
And sometimes, the fault it's not the people who choose to be like that, but the majority of societies, people who believe easily about what they hear and see. People who looking for an excuse to point the fingers at someone, blame and rate them.
(Just imagine how it feels when you get into jail when you've done nothing but you've been in a wrong place in a wrong time, there's a tone of examples, and then see how some will look at you when they hear you've been in prison, the looks, the fingers, the thoughts)
Now when we have such people, why shouldn't i stab people from behind instead of creating my own path ? Isn't it really easier ? The ground is ready with existence of these people. So it makes some so greedy to choose back stabbing.