This functionality just changed around Nov 17.
While I found the previous functionality - where when you wanted to find a rubric, all your courses appeared on the far panel to select from - was inefficient, especially if you wanted to reuse a rubric from a present course, the way this appears to have been "fixed" is almost worse. I DO like that all present courses are now listed - but there is no way to access rubrics from previous courses from here. The only way to include a rubric from a past course is to use the import method which is extremely inefficient. It means you have to get out of the assignment where you want to add the rubric and go to the Import Course content option > select the course > check selected content > Import > and then find the rubric you want (and you can't view it so that can pose some problems too if you didn't name it something pertinent).
THEN you import it - Go back to the Assignment - and finally go to +Rubric > "Find a rubric" > Find your course (that at least is easier to find now) > and select the rubric. That's a lot of steps.
What would make sense, as far as design - would be to still display the present courses and then have a link below to provide access to all the other course rubric folders.... like a "More rubrics" link. What's nice about selecting the rubric from here is that when you select a rubric, you can also see what it looks like so you can ensure you selected the one you want.