If you carefully read the agent's output you'll see why. It adds layers upon layers of workarounds and defences that hide serious problems, until the codebase reaches a point where the agent can no longer understand it and work with it. All the tests pass right up until the moment when adding a feature or fixing a bug causes another bug, and then nothing and no one can save the codebase anymore.

Maybe a year ago? Right now the LLMs I mainly use (GPT5.5, Opus 4.7) will intuit exactly what I need from my brief specs and universally go above-and-beyond in creating code that is not only extremely high-quality, but catches a ton of the gotchas I would have stumbled on, in advance.

Just a minute ago 5.5 looked at some human-written code of mine from last year and while it was making the changes I asked for it determined the existing code was too brittle (it was) and rewrote it better. It didn't mention this in its summary at the end, I only know because I often watch the thinking output as it goes past before it hides it all behind a pop-open.