Feels like the obvious reason is that you don't have the mental map usually created by figuring out and writing the code yourself. So, not only is it annoying to debug AI generated code, but you're left trusting that the system didn't sneak something in that you don't know about.

You can definitely help limit this issue by having clear instructions for how the AI should work, but there's just a feeling you're telling someone else what to write, while being left on the hook for it if anything goes wrong.

That and a lot of developers like programming, and vastly prefer to it to the alternative process of "acting like a virtual manager".