On the lighter side...
Maybe it goes totally against my nature, but I often wonder, 'Why do people feel the need to act like jerks'? Is it genetic or possibly a missing chromosome or two? Could it something you're born with, or is it learned behavior along life's way? Whatever it's origins, this an issue that needs to be resolved regardless of it's manifestations. Here is a brief look at a few of my suggestions.
According to Daniel Webster a jerk is an unlikable person; especially: one who is cruel, rude, or small minded. So with this definition in mind lets see how it may apply to the question at hand.
It seems to me being unlikable takes practice. Years of putting oneself first can lead to arrogance, that certainly could contribute to one's likeability. By mastering this character flaw one could easily become cruel as well as rude, and frankly, I would be surprised if they didn't. So maybe self-centeredness is the culprit.
But being a jerk still takes effort, an effort small minded people are unlikely to take. Small minded folks are selfish folks, and could not be bothered for a moment to consider another persons feelings, unless it was in there own best interest. So, maybe small mindedness is the reason for 'jerkyness'.
There is number of reasons that a person may feel the need to be a jerk, but none of them hold water in my book. Maybe they were dropped as a small child or neglected, you got me... But it must be very difficult leading a productive life, being self centered and small minded in a society of more than one.
So whatever the reason, there is no reason to be a jerk.