I didn't leave a downvote, but that sounds like a horrible policy. You'd get a ton of short comments on the least-valuable (as judged by voters) comments, bloating the comment tree and making it way less readable.
It is fortunate, not unfortunate, that YouTube prevents editing of the video itself after a video has been uploaded, viewed, interacted with, shared, commented on, and started to accumulate karma of various sorts.
It’s sucks for them (and their viewers). It doesn’t suck for viewers who want to see the thing that went viral - not some new video with product placement etc.