why is sour cream called sour cream?!

Because sour cream is cream that has soured.
It's regular cream that has been left out to be cultured by bacteria.
"Souring" is a common term used for this effect.

True sour cream is a dairy product made primarily of cream. It is very rich, high in fat, and quite adored by many. A similar product is the French crème fraiche, and in Mexico, the sour cream that tops many Mexican dishes is called crema Mexicana.

Adding bacteria derived from lactic acid makes sour cream sour. This is similar to yogurt, but yogurt tends to use other bacteria to ferment milk. The bacteria essentially culture the cream, causing it to become thick and sour. Untreated cream is quite sweet, but sour cream has that added zip which makes it so desirable to many.

I agree with Tom and others.
"Sour cream" starts as cream, then it's fermented (sometimes called "soured').

The process of fermentation makes things more sour tasting and also more acidic because the cultures/bacteria that are used will eat up the natural sugars (like the milk sugar or lactose in milk/cream) and turn them into lactic acid.

Fermentation makes milk last longer and be even healthier, but also makes it taste more sour whether it's done to make yogurt, sour cream, or other fermented milk products.
Sometimes sweeteners are added back in to compensate for the sourness (like commerical yogurts that aren't called "plain"), but sometimes not if the sourness is part of the taste desired. In the case of sour cream, the sourness isn't as pronounced as in plain yogurt for example because the cream has a lot of fat in it.

Fermentation is actually quite a widespread and interesting process and is used when making all kind of things like cheese, beer/wine, sauerkraut/kimchi, vinegar, soy sauce, pepperoni, etc.
http://en.wikipedia.org/wiki/Fermentatio…

It's like a heavy tasting plain yogurt, which is very plain tasting,

Awkward question?... XD

it fermented cream bacterial culture sours and thickens the cream

Because they let the cream sour and become less liquide.

Well done! Yes, it's because it's sour.

Yes, that's why they call it sour cream.

its sour