Because it was already grated, it could have picked up off odors and flavors from anything before it was actually packaged. Cheese is a fickle creature in this manner... It can pick up smells and tastes like a sponge and make it... well... gross

I try not to buy already-cut/grated cheese unless its necessary because of this very reason... often it's hard to get real Parmigiano-Reggiano cheese, and because it is stictly graded by a master cheese tester you can tell if you get an inferior one when you get a whole piece. The real cheese says "parmigiano-reggiano" all around the outside of the wheel. If the tester believes a wheel to be inferior, they will remove the name markings from the outside, which is part of the reason its often sold already grated, so that you cannot tell that it was removed. Inferior versions of this cheese can be bitter and taste off. What can I say, I'm a food geek lol
If you want the full info, check out this on Wikipedia...
http://en.wikipedia.org/wiki/Parmigiano_ReggianoPS It's named for the region it's produced in, not for a family name