Moreover, in our distant (according to the evolutionary tree) ancestors, the field of vision of the eyes did not intersect and signals from each eye came to different hemispheres of the brain (from the left to the right, and from the right to the left). Later, the eyes shifted forward, the field of view began to intersect and new connections were formed to the cross lines were added.
Because the eyes, of which there are two, do not create any picture, or visual vision. They create only continuous "signals" and send them to the brain, while the visual overview is built by the brain (1 piece), not the eyes.
Pictures taken from the retina of each eye are "mixed" in the brain - and as a result, we get a 3D picture. This is convenient for orientation in space.