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I could understand if it was no alcohol at all, but why only beer? I might be missing something, so if anyone knows...
Mail-order beer sales are only legal in about 1/3 of the United States. That makes advertising beer online much less profitable than advertising wine. Google may have decided it's not worth the aggravation of getting involved in a market sector where 2/3 of the clickthroughs are "wasted".
That said, it's their site. They get to control what's on it. Anybody complaining to the contrary is just a whiner.
Wine is considered an investment and commodity by a lot of people (as evidenced by places that I can have my wine shipped to for storage for many years until I can pick it up or wish to sell it to a 3rd party).
As it is an investment/trade good as well, many sites break the no tobacco/firearms/booze self regulating rules for wines and certain liquors (such as scotch).