I can understand why roulettes get locked like they are if ppl have purposely avoided unlocking ones they didn't like so they wouldn't have to do them.

I think the mentor roulette should still be the exception due to the purpose of it. Can't help any new players for content they're que'd for if mentors can't do the roulette because it's locked. Any newer mentors that have come about since the mentor system came around would still be looking at a wall of content to unlock it, that roulette is ment to help players with the new or returning status do content and the more mentors hat are able to do it the better.