It. doesn't. matter.

The only legitimate reason to make a rule is to produce some outcome. If your rule does not result in that outcome, of what use is the rule?

Will this rule result in people disclosing "AI" (whatever that means) contributions? Will it mitigate some kind of risk to the project? Will it lighten maintainer load?

No. It can't. People are going to use the tools anyway. You can't tell. You can't stop them. The only outcome you'll get out of a rule like this is making people incrementally less honest.