Because he sent funds to a contract (a program) and not a person (a private key). The operation of the given contract (the actual program) cannot be altered, which is useful in the sense that you can inspect the contract code and make sure that it does what you want with the funds you send to it.
Because he sent funds to a contract (a program) and not a person (a private key). The operation of the given contract (the actual program) cannot be altered, which is useful in the sense that you can inspect the contract code and make sure that it does what you want with the funds you send to it.