Im fine with reposts, even reposts without credit. But reposting a meme from one lemmy community to another lemmy community a day after the original and not crediting/cross-posting is just shitty and pointless. Sharing a meme to another platform is the digital version of telling a joke, sharing it to the same platform is the digital version of saying someone else’s joke louder.
I understand your frustration. It feels like stealing in a way, and a crosspost is a clean and neat way to share a post in a different community.
That being said, I don’t see it as a huge issue. Even setting aside that this particular user has a reason for doing that (which you might agree with or not), Lemmy is not that big that a few reposts feel like a problem, and having more activity is nice.