[DeadParrot]

I put this in the same category as why do castles and other fortifications exist in a world where spell or effects like teleport, rock to mud, passwall, summon earth elemental, etc exist.

It seems most fantasy settings wind up being based on real life Earth history usually from between 500 ~1200AD (before gunpowder becomes effective in siege engines). The setting designers then add a layer of magic to that Earth based setting without thinking how different things would be on Earth if magic existed. Look how quickly Earth culture has changed with the addition of the magic of Electricity. I suspect that similar changes would happen on any world where magic existed.

Either there are effective defenses against magic or anyone that can use magic is either killed upon discovery or wizards wind up running the place. Or the magical power is so small as to be mostly useless.

On Cidri, most metals other then Silver inhibit wizards. Not unreasonable to think that a door mostly made of iron might prevent the use of a knock or other spell if the wizard has to get close to cast. Also might imagine that one could construct a type of magical Faraday Cage that would block the passage of magical spells such as teleport.

I see no reason why a GM can't just rule that a bank or castle or similar contains such defenses against magic without having to create detailed explanation as to how such things work.