I'm not a moderator but have been one of the people rejecting your edits when I noticed them in the review queue, although the review queues require multiple reviewers to completely accept or reject an edit.
The default options in reject reasons include the one you're quoting and reviewers are lazy too, a custom reject reason requires additional effort. Sometimes I do bother to clarify briefly, sometimes I don't care.
Rejected by me with default reject reason 4 year old post and your improvement was 12 characters to the link of a link only answer that with our current standards should be flagged and possibly deleted.
Rejected by me with custom reason "Too little, too late. With 12 votes was already clear enough." on a 4 year old question.
Rejected by me with custom reason "Too little, too late." 5 year old question with 9 upvotes so clearly good enough a question at the time.
When I see a number of minor edits on old posts (several years old) from a relatively new user with low reputation they are "suspect". When the edit is approved the question is bumped to the front page and for instance questions that were already clear enough to have a number of up-votes, or their already accepted answers don't really need much mor exposure.
Such edits give the impression of a rep-whore. (To counter your comment about robo-voting)
Others my disagree. And since they approved the edits they actually did.