I don't really see how that could be done in a way that makes sense. If every time a profile was changed, the rejected merges went away, there would be no point in rejecting merges at all, because they'd just constantly be deleted.
You can always look at the rejected matches of a profile at the bottom of the page. Also, if you go to Find -> Pending Merges, set it to show only merges on your Watchlist, and then select rejected matches, you can see all the rejected matches on your Watchlist. And when you do a Find Matches search for all the profiles on your Watchlist, you can choose to include rejected matches in the search.
