First of all, the statement that says "practice makes perfect" was made by a normal human, like one of us (although he mustve been extremely smart though >.>) This statement is not ultimate, and like many others, contains exceptions.....
Now, why do we practice, you may ask?
Well, I believe that we practice to be better at something....... and the main goal in practice is not to achieve perfection. One should not think they can attain perfection just through sheer practice.
But nonetheless, we practice to improve, sometimes to be better than others, a rival, a friend, a stranger, whatever. Although human nature craves for perfection, it also wants more than anything else to be considered the best, to be recognised..... and that, I think, is what practice is for.