It’s weird to talk about them running low on mages when they’re in a time of peace and it’s been hinted that mages have been persecuted and imprisoned for political reasons just last chapter.
Remember what happened with Aura’s army, people. Because of the barriers, the demons haven’t been able to make any real headway into invading the humans. There are examples like with Stark’s village of small of small communities being exterminated, but I would guess that the humans as a whole just don’t feel the threat because their bigger cities are essentially safe (and that’s what made it possible for Aura’s subordinates to deceive their way into the city).
Considering both the desire for “elites” as well as the desire to limit the political power of mages, this exam is perfectly in line with the apparent political atmosphere of the world.