Ah, I think I got the source of misunderstanding: these mechanisms are not automated, but implemented as moderation guidelines and rules.

https://meta.stackoverflow.com/questions/421831/policy-generative-ai-e-g-chatgpt-is-banned

SO has mechanisms in place to filter out AI-generated content.

Editing any content to reduce its quality is considered vandalism and gets reverted on SO.

Except it’s not your data anymore. By submitting any content, you transfer the rights to SO.

Vandalism is always reverted on SO, even if done by the original author. No knowledge is lost. Suing OA for violating the CC-BY license might be possible, but I’d wager SO is not interested in suing them, and since they hold the rights, not much can be done by others.