The default somebody accepted three years ago is now the policy.
Every new team, every site, every shared link starts from a default nobody chose deliberately - often "anyone with the link can view," because that was the fastest option during a rushed setup or a project under deadline pressure. Whether the platform is Microsoft 365, Google Workspace, or something else entirely, the pattern is the same.
Sites and teams also get created faster than anyone retires them. A project wraps up and its team lingers, its files still shared exactly the way they were on day one, discoverable by search long after anyone remembers why. Reminding staff to "share responsibly" doesn't fix a default that was never actually decided.
Collaboration governance treats the sharing default, the creation rule, and the retention period as decisions with a named owner - separate from which chat or file-storage product happens to be running underneath them.