Bacause He created you. That is why you owe God worship.However, if you believe that you evolved from the goo, through the zoo, to you, then why even bother ask the question?
God seems rather insecure if he demands worship for the act of creating us.
God creates humans with free will and then tells us that if we use that free will in a way that breaks his illogical and arbitrary rules, he will damn us. I simply don't get it. That's selfish and childish. Sounds like god has "little man syndrome," also known as "Napoleon syndrome."