A better answer would have been "the term 'request for comment' is historical, dating from a time when the preferred way to make a formal comment on a document involved writing another document, which then was numbered into the series". That mechanism is still available, although usually very slow. But documents that become RFCs are now first posted as Internet Drafts (see http://www.ietf.org/ID); comments on those are both solicited and, usually, handled very quickly.
Today, the RFC Series, despite retention of the original name and numbering series, acts as a permanent, archival, repository of information, decisions taken, and standards published. As such, documents in the series are subjected to review and editing processes (which differ somewhat depending on the type of document and are appropriate for conventional references from conventional documents. Running conversations, logs of comments, etc., are not well suited for that archival and reference role, regardless of their other advantages and disadvantages.
Could it not be useful to have a "List of Comments" (LOC) for each RFC? Where experience about the RFC reading, testing and implementation could be listed by the authors (or a successor) from experience and questions received. It would avoid the same questions to be debated again and again and it would help further thinking. These comments could start with a summary of the WG debated issues, explaining the whys of some options. I suppose the implementation would be easy enough since it would follow the same numbering scheme and titles. Such a LOC being an updated appendix could be reviewed and help preparing replacements.
jfc