Because Lemmy doesn't have nearly the same level of bots/ai accounts literally dredging up comment chains that are 1) deleted and 2) decades old. This means that someone can repost something from reddit, then train AI on the very real (and new) human being responses as opposed to whatever inane bot threads that spawn on reddit these days. More accurately they can refine what they've already trained on reddit against these new responses.

That's one problem. Another is that reddit sucks and if you want Lemmy to be reddit 2 you can fuck right off back to reddit (or facebook, or x, or whatever).