Likely because it's blatant misinformation and very spammy. Licences permit additional use, they do not restrict use beyond what copyright already does. I imagine there'd be fewer downvotes if they didn't incorrectly claim licencing their content was somehow anti-AI. Still spammy and pointless, but at least not misinformation.
Imagine if someone ended every comment with "I DO NOT GRANT PERMISSION TO LAW ENFORCEMENT TO READ THIS COMMENT. ANY USE OF THIS COMMENT BY LAW ENFORCEMENT FOR ANY REASON IS ILLEGAL. THIS COMMENT CANNOT BE USED AS EVIDENCE AGAINST ANY NON-LAW ENFORCEMENT PERSONS IN RELATION TO ANY CRIME."