Why does the "right" represent good and the "left" represent evil?

Throughout history, many cultures have regarded the left hand and left-handedness as evil. This tendency can be seen in the dual meaning of the word left, in the etymology of words such as sinister, which in Latin means both left and unlucky. Consequently, the left hand has often been used as a symbol for the rejection of traditional religion. The word right as used with hand in the Old Testament is generally the Hebrew word yamin meaning stronger, more dextrous. The word for left is smowl meaning dark. Much of this has been contributed by the practice in many cultures of using the left hand to cleanse oneself, thus making the hand "unclean".

https://en.wikipedia.org/wiki/Left-Hand_Path_and_Right-Hand_Path

Left is also referred to as sinister sometimes, mostly back in medieval times. Since sinister is also a symonym for evil, that could be the reason. I don't know if this is why or not, but it's interesting theory.