They're deprecating all the completion/edit models.
The chat models constantly argue with you on certain tasks and are highly opinionated. A completion API was a lot more flexible and "vanilla" about a wide variety of tasks, you could start a thought, or a task, and truly have it complete it.
The chat API doesn't complete, it responds (I mean of course internally it completes, but completes a response, rather than a continuation).
I find this a big step back, I hope the competition steps in to fill the gaps OpenAI keeps opening.