You don't have to, you can write it by hand. I thought we were talking about how we can make computers write code, instead of humans, but it seems that we're trying to prove that LLMs aren't useful instead.
Isn't this something that we should have doing for decades of our own volition?
Separation of concerns, single responsibility principle, all of that talk and trend of TDD or at the very least having good test coverage, or writing code that at least can be debugged without going insane (no Heisenbugs, maybe some intermediate variables to stop on in a debugger, instead of just endless chained streams, though opinions are split, at least code that is readable and not 3 pages worth per function).
Because when I see long bits of code that I have to change without breaking anything surrounding them, I don't feel confident in doing that even if it's a codebase I'm familiar with, much less trust an AI on it (at that point it might be a "Hail Mary", a last ditch effort in hoping that at least the AI can find method in the madness before I have to get my own hands dirty and make my hair more gray).