I'd say this is because the join itself is defined in the attribute view (internal name for that is column view type "join").
Look, the main purpose of attribute views is it to be used in conjunction with analytic views.
To me, the referential join is not that particularly exciting, since most of the time, you cannot guarantee that the pre-conditions are actually met.
And if you cannot do that, this join is simply not to be used, as long as you're interested in correct results.
- Lars