My theory on this is that apple is one of the few companies where everything they build seems to be well integrated into their ecosystem. This is part of their appeal.
Another part of Apple's appeal is that they've positioned themselves to appear as the company that cares the most about consumer privacy and security. Lockdown mode seems to be one of those features that's great for marketing and PR in certain circles, while being extremely useful in situations where it's needed.
I imagine someone writing an article claiming how lockdown mode saved them, and that's practically free viral marketing in the security circles.