Most employees don't make up rules to assert their authority.

If a rule is made up, it's likely to ultimately benefit the most passengers (one item in OHB) or ensure that no regulations are violated. Delta's rules about pets-in-cabin are stricter than the DOA to make sure that no one breaks the rules.

They only call it a rule or policy because if they don't, no one listens. Most people don't even listen when an employee makes mandatory announcements.