I understand why I cannot flag a comment I've upvoted. When I upvote a comment, it means I think it is of especially high quality.
But an especially high quality comment can become obsolete (for example, if a question is posted that contains and expands on the same information, or if it requests additional details subsequently provided by the OP). Then, it seems to me that I should be able to flag the comment as obsolete, even if I cannot flag it as anything else.
Is there any good reason why we cannot flag comments as obsolete that we have previously upvoted?