Why is there an expiration date on sour cream?

Hey, Matt:

Why, why, WHY is there an expiration date on sour cream? It's already sour.

-- JBee, Encinitas

It's already a little sour. After three weeks or so, it gets reeeeeeely sour. Then the bacteria take over. Then the mold grows. Then you find it hidden behind the dead lettuce. Then you'd better throw it out.