When comments first rolled out and you could upvote them, there was no option to undo upvotes at all. They were permanent. It was argued that, especially on mobile devices, it was easy to accidentally click on an upvote for a comment you did not intend to cast and it was then impossible to undo it. So we expanded upvoting comments ever so slightly to allow immediately undoing a comment vote, under some conditions:
- You must still be on the page and cannot have refreshed.
- You must undo it within a minute of casting it.
- You can never upvote the comment again once it's been retracted.
We do not have any interest in further expanding the functionality behind comment votes. The ability to undo a vote on a comment was already a compromise on our part meant only to address users who accidentally upvoted a comment when they did not mean to do so, as mentioned above.
The locking mechanism is intentionally short and unforgiving because we assume that you would only ever undo an accidental vote on a comment immediately after accidentally casting the vote, because that is the only use-case we recognize for undoing comment votes.
Regarding your specific suggestion: Comments can only be edited for up to five minutes after they are posted, at which point they would never be edited again (barring a moderator edit, which is extremely rare). Thus locking comment votes until they've been edited would mean that few comments could ever be unvoted and would explicitly disallow undoing accidental upvotes in many cases.