We trained agents on millions of pages of documentation telling them to write good comments and good code and then we tell them never to write any comments.
It’s almost the “we built a robot who loves to play Sonatas and gave it no hands” type of thing.
Being overly trained on comments in documentation could be one of the reasons why Claude models write frustrating comments (which often manifest as written justifications of how the code satisfies the prompt). A comment in a tutorial is going to be geared to explaining how the code relates back to the tutorial task or restating what the code does, rather than documenting the "why" of surprising code.
What models are you using? I've had "Never add any new code comments" in my system prompts for like a year at this point, seems every model above 14B picks this up just fine. Are you using llama 7b or similar for testing this?