It wasn't that the Academy wasn't safe. Considering many human factors, it was.
Taking the kidnapping, for example, it wouldn't have been as easy if he were in the academy grounds. No matter how powerful or informed the enemy was, unless they had authorization, they wouldn't be able to get in.
The same was the case for monsters and beasts.
And while the palace had its own safety system, if someone from the inside wanted to cause trouble, they could for sure.
Staff at the academy simply didn't have the time to waste, nor the need for it. There may or may not be occasional 'setbacks', but the chances of getting caught were much higher.
But warding was something that protected against other things. Like not allowing monsters to gather in the first place or clear out any harmful energy. It spread out across the area even beyond the boundary and ensured that even if something went wrong, this would be the last place affected.
