When you let an LLM author code, it takes ownership of that code (in the engineering sense).
When you're done spending millions on tokens, years of development, prompt fine tuning, model fine tuning, and made the AI vendor the fattest wad of cash ever seen, you know what the vendor will do?
You have to migration path. Your Codex prompts don't work the same in Claude. All the prompts you developed and saved in commits, all the (probably proprietary) memory the AI vendor saved in their servers to make the AI lock you in even more, all of it is worthless without the vendor.
You are inventing "ah heck, we need to pay the consultant another 300 bucks an hour to take a look at this, because nobody else owns this code", but supercharged.
You're locking yourself in, to a single vendor, to such a degree that they can just hold your code hostage.
Now sure, OpenAI would NEVER do this, because they're all just doing good for humanity. Sure. What if they go out of business? Or discontinue the model that works for you, and the new ones just don't quite respond the same to your company's well established workflows?