> telling maintainers how to act will not fix anything.

That depends. In this case it's good actionable advice that should hopefully lower cognitive load. Politely suggest a fork, then if the nagging persists block and move on. Sure if you're in a position of authority you have a responsibility to the community but cutting ties with a stranger who is flagrantly violating social norms is perfectly acceptable. There's no expectation that you indefinitely burden yourself with their poor behavior.

Sometimes dropping the ban hammer really is in the best interests of both yourself and the project.