I wonder if it's because there's something secret in those rooms they don't want us seeing, or if they're just trying to keep us all in a smaller space. To make us easier to keep track of. They're definitely not locked and reinforced by normal means, though.

[ Again, Orpheus suspects it's because the Wizard is a god, but he's... not going to mention that to Peregrine, even if she did apologize after seeing what happened with the knife and the earthquake. ]