A rule that's doing its job doesn't get announced, because nobody's worried about it. Think about your office building. There's no sign that says "We promise not to lock the fire exits." The fire code covers it, and so does habit. Now imagine the tenants asked the building manager, in writing, whether the exits would stay unlocked this year. The manager's reply doesn't tell you much, but the question does. Something gave the tenants doubt, which created the need to ask.