Why aren't headphones already equalized?

Why don’t headphone manufacturers produce headphones that are already equalized? They probably would if they could. Unfortunately, it's not that simple. There are lots of subtleties and variables that go into making a pair of headphones. Realistically, engineers can’t ensure that the end-product will reflect their intentions verbatim. This is where equalization comes into play: it allows you to smooth out imperfections and, in the end, get you more of your money's worth out of your headphones.