Why can't a owner / reviewer add another reviewer to a branch?

As a designer submits a branch review and adds a reviewer to it so they can take a look … Why can’t the reviewer who was invited, add another reviewer to it?

Only the initial designer can do that … As a reviewer/editor; I want to invite the Product Owner later in the process after I look at it so they can only be notified when its their time to do so.

Is there any reason why an added reviewer to a branch, can’t request others to review besides the OP designer that requested it? What if the manager/reviewer want’s a second eye on it and not have to tell the designer to then go add someone again?

Doesn’t make sense why we wouldn’t have that option (yet any editor can still merge whether if they’re invited or not). Now, we would have to tell the person who submitted it to add another person when the admin / manager should be able to do so too.