There is no definitive answer yet to the question why the human brain likes all things symmetrical.
Symmetry means order and implies some kind of efficiency. May be we like symmetry because our body is organized along binary pairs. As all of our pairings are mostly not entirely symmetrical, our eyes are not exactly the same for example, it may be that we long for the ideal and therefore when we see it, we instantly like it.
original art & motion by whornung