The rationale is explained in this 2015 commit: https://github.com/coreutils/coreutils/commit/35217221c211f3...

The current implementation is much faster than in that commit on GNU/Linux, as documented in this 2026 commit: https://github.com/coreutils/coreutils/commit/2b1c059e6a06ee...

The OpenBSD implementation is much slower than both the GNU versions from 2015 and 2026. However, their goals are different from ours, and that statement should not be interpreted as criticism of theirs.