It doesn’t, quoting strings does solve almost all issues, but it does leave potential footguns for the future.

If you don’t enforce it, in the future the “subset of YAML” property might get weaker, especially if someone else is modifying the config.

If you treat config files the same as code, then using a safe subset of YAML is the same as using a safe subset of C. It is theoretically doable, but without extensive safeguards, someone will eventually slip up.