Well, that's why I said "mostly". The thing I need to protect, the key, is a very specific piece of data, which is used for one specific purpose, and I can take specific measures to prevent that secret from leaking. Everything from not writing it down, to key-sharing, to physical lock boxes with multiple locks, to offline-only storage, etc. It's much harder to do any of that with blueprints, since blueprints have competing needs -- they are no good if locked in a box most of the time.