It is specified this way on OpenBSD: https://man.openbsd.org/man7/hier.7

> /bin/ User utilities fundamental to both single and multi-user environments. These programs are statically compiled and therefore do not depend on any system libraries to run.

> /sbin/ System programs and administration utilities fundamental to both single and multi-user environments. These programs are statically compiled and therefore do not depend on any system libraries to run.