Replying to a previous posted note with clarification is a way of adding context. I enjoy screen captures of posts that big shots put out on x and later deleted. Shows the character of the people influencing others. Your notes can be saved by anyone with or without the memory hole button. 'no delete' as a feature not a bug.
Yeah, that sounds great until you realize that your reply is lost in the replies and doesn't really add context for that reason. This has already been written about by @rabble and he makes better points.
It's neither a feature nor a bug.