I'm much less likely to comment on a post if I've seen that someone already brought up my point (or something close enough to my point), even if I might have expressed it differently and any resulting discussion if I had commented might have spun off in a different direction.

If everyone's reading the same post, then if you had spoken up, any interested parties would have heard you, just as the first commenter was heard. If post is split up, there's no guarantee that you'd be on a different site than the first commenter, and there's no guarantee that anyone who spoke up would be heard by any of the potentially interested parties reading the post.