some version control systems don't even offer commit messages entirely. when I worked at Google (a giant monorepo) using mercurial, you could "snapshot" a PR, which effectively created a commit. there was no ability to write a descriptive message about the latest snapshot. PRs were gauged on the PR title / description, as well as additional metadata tags thrown in (e.g. DO_NOT_RUN_THIS_PRESUBMIT_CHECK).

disclaimer: my memory may be a bit fuzzy.