Some communities have bots that copies posts from Reddit. Some do that so there would be more content in Lemmy. Those bots probably don't break any rules set by the Admins of those instances.
Personally I don't like that content is being copied without the permission of those who made the posts in Reddit. Also, in some cases it sort of defies the whole point of the community. For example, one of the Explain Like I'm Five communities has a bot like that. The bot includes a link to the original post. Why would anyone reply to the bot's post, when you can just read the explanation from the original post? That doesn't help make Lemmy more active place when a bot posts things and no human ever replies to them.