As far as I understand, the imbalance of the two hands is due to the collaborative nature of a species (if I teach you something is easyer if we use the same hand). There are advantages of using the other hand as dominant, in fact in competitive environment like ping pong we see a 50-50 split between left and right hands. This is because the left hand has the advantage of being rare and so the majority is not trained to compete against the minority, while left hand people mostly compete against right handed. If two lefties face each other they are equally disadvantaged, that's why in the end a 50 left 50 right distribution emerges.
Also fun fact, kangaroos have this same 90-10 split: https://www.nationalgeographic.com/animals/article/150618-ka...