Annex K (which is what that is) is sufficiently unpopular as to have been under discussion to be removed from the standard. Few implementations exist, and even fewer conform to the standard (e.g. Microsoft's doesn't).

https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1967.htm

Furthermore, since the kernel uses no C library, it's the kernel developer's choices what to implement and use.

> Should be using strcpy_s or strncpy_s

These functions are optional in the C standard and not always present. AFAIK, they are not included in glibc as of 2025.