Because GOD cursed the ground, not humans. But I warn you my interpretations are just that, mine. I take them from my own literal readings. I believe that most of the fundamentalists are not reading it literally enough.
I believe the bible is written so that it be understood on several levels at once and one of those levels is the literal. I sometimes use the idea of a prism. You might see red and I might see green from the same prism and we are both right but the original light is white.