Accident of evolution most likely. The left side of the brain controls the right hand. Humans went through a bottleneck event about 70,000 years and and the population of humans almost crashed. Possibly the hand preference was something that made it through the bottleneck in a genetic drift event so that descendents from that time on were more inclined to be right handed.
The exact and real reason seems to be quite the bone of contention among several scientific disciplines..
Living in a right-handed society, this can be a problem for left-handed people because so many things including buttons, door handles and scissors are designed for people who are right-handed. Although scientists have a good idea of why some people are left-handed, they have yet to discover the precise details and reasons why they differ to right-handed people.
However, it has been noted that left-handed people are much more creative and intelligent than right-handed people. Some famous figures such as; Bill Clinton, Ronald Reagan, George W. bush, Julius Caesar, Queen Victoria, Henry Ford, Prince William and his father Prince Charles, Julia Roberts and Einstein were all left-handed. There is even a national day dedicated to left-handed people which is August 13th.