Let’s face it: The Japanese are the kings of advertising:
Yes there is an explanation and first of the two styles are “Contential” and American (also known as zig-zag in high dinning practice). Contential style derives from the medieval courts of Europe. Here peasants would use their hands to eat but royalty would use utensils. While the utensils where used to eat properly they could also be used as weapons against the Royal Court thus a system of dinning was set in place as to deter this malcontent. With proper Contential style of holding the fork in your left hand with prongs down and knife in your right with the blade down or pointed inward and both fork and knife balancing on three fingers and with proper posture it is quite hard to stab anyone. Also, if you were to attempt to stab someone from this position it would have been recognized by the guards in time to save the court. So this is how the European called “Contential style developed.
As for the American or zig-zag style this derived from the late entry of the fork. Most meals in early America contrary to popular belief required only a spoon to eat. All foods were pre-cut and mainly in stews. Thus, it became practice not to have your left hand on the table because it had no function and gave one bad posture.