Why do human have foot arch?

A healthy arch supports itself so arch support is not needed; the weight is distributed between the forefoot and the heel by the arch. The arch is held by muscles and ligaments, this means that with training you can help build it up. read more

However, human feet, and the human medial longitudinal arch, differ in that the anterior part of the foot is medially twisted on the posterior part of the foot, so that all the toes may contact the ground at the same time, and the twisting is so marked that the most medial toe, the big toe or hallux, (in some individuals the second toe) tends to exert the greatest propulsive force in walking and running. read more

There is also a difference in how the bones are turned when it comes to pressure being exerted. When walking quadurepedally apes do not need "arch support" because branches are being grasped. Their feet then serve as an extra set of hands. We on the other hand(or foot haha) have three arches. read more