Because I Said So!
After creating heaven and earth, God created Adam and Eve. And the first thing He said to them was, "Don't."
"Don't what?" Adam asked.
"Don't eat the forbidden fruit," God said.
"Forbidden fruit? We got forbidden fruit? Hey, Eve! We got Forbidden Fruit!"
"Don't eat that fruit!" said God.
"Because I'm your Creator and I said so!" said God, wondering why he hadn't stopped after making the elephants.
A few minutes later, God saw the kids having an apple break and was angry. "Didn't I tell you not to eat that fruit?" God asked.
"Uh huh," Adam replied.
"Then why did you?"
"I dunno," Eve answered.
"She started it!" Adam said.
Having had it with the two of them, God's punishment was that Adam and Eve should have children of their own!