This question is perhaps the most interesting question. The short answer is because they are supposed to be dismissed.
As an example, when the sign says "No Parking" you may actually be allowed to park your personal vehicle there while quickly picking up a passenger or dropping off a passenger. The Law is on your side even though the posted sign that says "No Parking" doesn't say what the underlying rule is. Perhaps you are wondering why the posted Sign only says "No Parking" and not the entire rule?
That is a great question...why don't the posted signs state the complete rule? Because City officials want to make it difficult and confusing for both residents and visitors alike.
Our job at parkingticket.com is to inform you about the entire rule and if the summons should be dismissed according to those rules.