Hi. Thanks for the comment 🙂 When they use someone else's work, they can simply mention that the content is not theirs. If they don't mention, they automatically claim the authorship of the content and deceive readers into thinking that they the are the authors. If plagiarised content is not tractable to the original is irrelevant. Poetry, articles, memes, tales, photography, art, jokes, etc. Memes are not any sort of exclusive and extraordinary content to get a jail free card. Hivewatchers have been explaining why it's abuse since it was created in 2016. If some content isn't traceable to the original author is irrelevant. It doesn't take any effort to simply mention the source from where the content was copied and pasted from to point out honestly that they aren't the authors. Rewards weren't declined, source of copying was not mentioned/non authorship wasn't mentioned so the content was deception towards readers and abusive activity to gain monetary and/or social reward. Also, even if the source of copypasta was mentioned but there's no significant personal thought added to sourced-shared content, it could be considered as no effort copypasta spam to fish for rewards (unless rewards declined).

I personally often use other's content when create a collage on social media including using memes. If I can't trace original source, I simply write in sourcing "Original Source of meme: unknown". In this way, my readers know that I didn't create it and I'm honest about all content used and clear about what was of my creation in collage.