Every castle wall can be broken with money.

How much money is required to decrypt a file encrypted with a 256-bit AES key?

How much person(s) who know the key will take to change country and don't work anymore?

Or how much it is cost to kidnap significant one of key bearer(s)?

I think, it is very reasonable sums for governments of almost any country.

I think you assume that encryption keys are held by people like a house key in their pocket. That's not the case for organizations who are security obsessed. They put their keys in HSMs. They practice defense in depth. They build least-privilege access controls.