When is a rule not a rule?

Just got back from Cromer Seacroft site where there are two notices at the entry stating “Sorry no arrivals before 1.00pm”. However on at least two occasions we witnessed people, not only arriving before 1.00pm but being booked in and allowed on site, why do I bother timing my journeys and / or stopping in lay-bys to ensure I arrive after the advertised time when the rule is so blatantly ignored by others (including the wardens who allow it to happen)? 🤬