[Namidairo]

You're assuming that flash storage is the only thing to be concerned about in a secure boot scenario.

Assuming that the platform is even secure boot capable, you'd blow a fuse or similar at the factory to put it into production mode.

However even then, secure boot isn't infallible. Either they're implemented shoddily, or you end up power glitching past verification.

(I've seen a certain vendor who's name starts with Qualco... fail because they didn't remember that u-boot was... configurable.)