Why is there an expiration date on sour cream?

Haha - good question. I can only guess that because it is a dairy product, it becomes dangerous after a point even though it is cultered. I have never researched the chemical processes of milk but I know that it becomes deadly with bacteria. It is pasteurized to become safe milk and cheese, cultered into yogurt and sour cream, whipped into butter and cream - whatever the process and end result, diary products do not have a long shelf life before they become infested with harmful bacteria. I'll be interested to read what more informed responses have to say.