Let me explain. There are two most vulnerable parts of the body: the heart and the brain. Now the heard is buried inside the chest and protected somewhat by the ribcage. But the brain... the brain is protected by a shell of bone (the skull) but it sticks out on top on the end of an appendage (the neck). And the neck, to be honest, isn't that tough.
And, because the brain needs a lot of blood, and it is farther from the heart in the head, critical veins and arteries run through the neck. Not to mention nerves.
Now, maybe evolution thought our eyes should be high up to see threats better. And, for some reason, wanted a short run of the optic nerves. (Actually, I read somewhere that the optic nerves and the retina are extensions of the brain.) So it put the brain high as possible. And, apparently this is helps with survival more than protecting the brain like the heart.
So maybe evolution didn't mess up.
What do you think? Let me know in the comments below.