The chips do not have an unique identifier on them. It will be impossible for the manufacturer to look at a chip and then query their db for the encryption key. At best they will be able to provide all the encryption key that they have produced possibly reducing the search space form 2^128 to ~10B. Also, secure enclave manufacturing process is done is such a way that even the manufacturer does not know what the key is. They don't generate a key for each chip, a natural phenomenon which is truly random is used to burn in the encryption key.