I wonder this too. I prompted Opus 4.7 to generate some Python threading code for me. The code to run the sub-thread looked like this:

    def run():
        with contextlib.suppress(SystemExit):
            do_thread_thing()

    threading.Thread(target=run, daemon=True).start()

Suppressing SystemExit was surprising, and made me curious. I followed up and asked the model: what's the purpose of that?

The model's response: "Honestly? Cargo-culting on my part. You should remove it."