Trouble with replies is that:

1. They're not as visible as the post they're attempting to moderate, so people just won't notice that there's more info.

2. Many people practice https://indieweb.org/POSSE so you now need to duplicate your reply across many separate social networks if you're going to match the reach of the specified content.

The nice thing about a plugin is you can associate the annotation with the underlying content by CTPH hash (i.e. the underlying tech for virus signatures) so it shows up wherever the annotated content shows up, regardless of URL and and with identical visibility since you're going by what appears on the screen not by whatever internal logic the underlying site uses.