The website clearly states that rubrics cannot be imported into Moodle Workshop. If this is indicated on the website, meaning the developers are aware of the issue. Why is this not addressed?
It is surely a question of priorities. There are many proposed improvements on the Workshop roadmap but Workshop is a fringe activity in comparison with Forum, Assignment, Quiz and some others.
Furthermore, it is a complex activity and probably not so easy to refactor.
David Mudrak, the lead developer of the Workshop activity, will confirm (or not) my intuitions.
(Thanks, David, for this wonderful activity.)