Sour doesn't mean bad-contaminated-moldy-poisonous.
Because it goes off like everything else and when it does it tastes nothing like it should trust me!!
So you don't eat bad sour cream, presumably.
That's the date to use by for maximum flavor or quality. It doesn't necessarily mean it will go bad then.
And why on cheese? Proper cheese is matured for ages in cool (but not cold) conditions. Then they pack it and it supposedly "goes off" in a month or two. It is just a means to get you in the fr<x>ame of mind that anything out of date should be thrown away and more purchased.
After that date, the wrong kind of bacteria will begin to multiply in it. There is the mold factor too. It is cooked to kill the culture bacteria before it is packaged. Ditto for cottage cheese. I worked as a maintenance man in a diary, for 8 1/2 years. I lost about 15 pounds within a month after I left there.
So you don't accidentally go and eat it when it sourer.
All products settle and taste different even if there not expired, so they do they so the customer doesn't ask for a refund