The problem is, these statistical "AI" models actually do pretty significant factual errors.

If you let it, for example, design yourself a rocket engine there is a fairly high probability that it will explode when you actually build such an engine and switch it on. Most of the engine could be "correct" but all it takes is an error and you get potentially catastrophic failure.

Might not be a problem with a small and cute little toy robot. Might get someone killed with an industrial robot.

So yeah, sure, you can let one of these design you a robot. Or some action the robot takes. But you need an actual human expert who knows what he/she is doing to "proofread" the output and correct the errors in the design or action.