BSD is useful for when you want to program some specialty hardware once and chuck it into the abyss with no updates and without releasing the source code so you can maintain a barely passing level of security through obscurity. Or if you really just don’t want to publish your source code for a unix system.
Things like modems and old routers come to mind. Also PlayStation iirc.
Most modern IoT stuff I’ve messed with uses linux probably because the devs like not having to manually package things and deal with weird edge case bugs. Since they’re usually making software updates anyway, published vulns are less of a concern.