It's one thing to say "I made this" somewhere else, where there aren't posting rewards. It's still not cool, but nobody's necessarily benefiting from it besides a hollow boost to the ego.
I disagree with this statement. Most published content on the Internet ends up getting missed or ignored. If someone reposts material from years ago that is still valid and is theirs, it is a good thing to have it on the blockchain instead of having it get passed by or removed.
You don't seem to be talking about plagiarism. That's what I'm talking about. If you go somewhere else, say "I made this" and then post someone else's art for instance, it's plagiarism. But it's not considered as big of a deal, because the stakes are low. Steemit is different.