I think it should help to prevent spam. A spammer can only write 3 posts in 1 thread and then has to stop. … If others read the thread they will identify the spam and it can be removed. …
I also had this issue once. For me it was possible to edit my first post and add the content of the second post to it. So I had 1 more left
I know with your posts that wouldn’t make too much sense, since it is a reply to 3 different posts from different users. … But it would be possible to reply to several users in 1 post … I also think that’s sub-optimal.
I think it’s a very similar measure than the 20 character limit. 20 chars disallows posts with an eg: +1 in it, because we have the emojis for this type of posts.
I personally would like to up the limit to eg: 5 and we will see what happens.