Nobody talked about granting monopoly, it's just about common courtesy really. They basically strung him along before cloning his tool in the dark, when they could have done it in the open in various different ways. After the failed hire, just give him a heads-up like "hey, we really like your stuff but for various reasons we can't hire you and we need to rewrite it, what about we make this manifest a bit of a common standard? We'll credit you for that", and then everyone is happy.