OpenBSD is much more open (pun not intended!) about breaking parts of userspace to push through beneficial changes. After all, they control their own userspace and can fix up most things before they even become an issue. Linux is only the kernel.
They could, but their users really won't like that. They have their workflows that they got used to. In practice it's gonna be GNU Coreutils and Glibc and the other usual suspects. If they bundle something more exotic, it better be for a very good reason. For example musl on Alpine or what Android does.
