Feeds are littered with repost bots recycling mindlessly internet trash. Not rare is to see series of exactly same posts from different communities with no comments.
I think reddit bots are there to promote specific content and create a synthetic sense of engagement, which spurs organic engagement. Its part of the business model.
I have a conspiracy theory that this is how Marvel got to be what it is today.
I usually find it difficult to tell if I'm interacting with a bot on Reddit (unless it's of those novelty bots with bot in the name). I think there are definitely a lot of higher quality bots on Reddit that are designed to hide their true identity and intent whereas on Lemmy the bits tend to be more obvious and visible.