Thing is, it’s used for a lot of other shape parameters as well (like size, feathering) which it really can be useful to retain between images/sessions. For example, I most commonly use retouch for removing dust spots and only very rarely change the default start point (size, feather) for a circle mask, once I’ve set it. To single out just one of the many shape parameters and say “this one works differently” seems worse.
(Edit: stuff like this is why I spent months rewriting the user manual but unfortunately I can’t make people read it)