The problem: the roster is a person, not a system
In most staffing, nursing and facilities operations, the roster lives in one coordinator's spreadsheet and one coordinator's head. They know who is qualified for which site, who cannot work nights, whose licence is about to expire, and who will actually answer the phone at short notice. It works until that person is unavailable, and it never scales past a few hundred staff without overtime and gaps becoming permanent features.
Compliance is the sharper risk. Credential expiry dates sit in a folder. Rest-hour rules are respected when someone remembers to check. Attendance is reconciled against the roster days later, by which time a billing dispute with the client has already started. None of this is negligence; it is simply more moving parts than a spreadsheet can track honestly.