I do agree on each and every single point here. I think the post missed to explain this properly and I am gonna edit it asap.

We don't encourage adding comments for "rejection" since different frontends are used where the "rejection" mechanism does not exist and may harm the user at the end leaving a "rejection" comment without an current implementation in our interface for that.

We will make sure to provide valuable and informative comments in any case to help the contributor improve, whether the post will be eligible for an upvote or not.