If someone obtains the repository, whether a leaked backup, a breach at your git host or an ex-colleague's old clone, they can attack the encrypted keys offline, for as long as they like, on hardware that keeps getting faster. Nothing expires; there is no server to lock them out.
The only real defence is how hard your unlocking key is to guess, which is the strongest practical argument for hardware or KMS custody over a passphrase. A passphrase can be attacked. A security key cannot be attacked at all without physically having it. If you keep production credentials in a vault whose members use passphrases, you are betting on those passphrases against unlimited offline guessing.
"Future hardware" includes quantum computers. If one ever breaks today's public-key encryption, the wrapped keys in every old copy of the repository break with it, and nothing can be recalled. The format is versioned so the encryption can be upgraded ahead of that, and the design document proposes adding a quantum-resistant layer to the key wrapping before version 1.0.