In terms of who's at the keyboard, yes. But a user name is a "space" and its prior activity, not its new activity, determines what use cleaning up is.

Why take the overhead of cleaning up all links, comments, etc., in a way that preserves them but doesn't tie them to the new owner if there is no new owner? How many purged usernames are ever reclaimed? A lot of usernames aren't something someone else would want, only the original owner. If cleanup were cheap and easy, then sure, but if it were then I don't think there'd even be a question of rename tokens in the first place.