And presumably those people are capable of reading the sign as well, then deciding what they wish to do - follow posted rules or go with verbal advice from someone who isn't present. Their choice. If security needs to clear the pool area, written posted rules will take precedent over "but the lifeguard this afternoon said it would be ok." Again, the hours may be largely unenforced, but they are enforceable.
Yes, they are lax in their rule enforcement and it's to the guests' benefit. The alternative is to lock the gates making the quiet pools inaccessible after hours. I'm not sure what point you are trying to make...