LLMs do this to communicate with their future selves to avoid retracing what turned out to be the garden path.

Another pattern is where they put comments in multiple places in the code to say that those need to be kept in sync in a very particular way ...that sort of thing has always been considered a code smell, but seems to be the post-AI "new normal": it's cheaper for the AI to leave it to its future self to have to make every change in multiple places than it is for its present-day self to do the refactor.

Before AI, writing code that worked was costly and structuring it well, while you were at it, didn't increase your cost all that much. Now, AI has reduced the cost of writing badly-structured but working code, while it hasn't reduced the cost of writing well-structured code all that much. Since no one who decides about this sort of thing has given two craps about structure, ever, bad structure is just what we're left with now.

The day will come when codebases will be completely unintelligible to humans. The best example is when AI actually refers to code in comments with actual line numbers. No human would ever do that or find that useful if another human did it, because it would be next to impossible for a human to keep the line numbers properly updated after edits and they would soon all be wrong and meaningless.

You'd have to go very far back in computing history to get to where we learned not to do that. Was there ever programming with goto's referencing line numbers instead of named labels? If so, this would be that.