The outcome might not be deterministic (edge-case, race condition, weird error path). This is also true with human but at least a decent engineer can sit in a review board walking through their reasoning on why did they do what they did and their rationale

Good luck asking AI on "why use X, why X and not Y", yes they will answer but it is based on their current, ad-hoc deductions, not their past reasoning

I guess the same can be said for legacy code base where the original author had left years ago and currently running a kebab shop in Dagestan but my point still remains