?The reason it's called "whole milk" has less to do with its fat content, than the fact that it's comparatively unadulterated. As the Dairy Council of California puts it, whole milk is "the way it comes from the cow before processing."
While that's not entirely true, it does capture the gist of the justification. Whole milk is whole because it is — for lack of a better word — intact. "2 percent," "1 percent," and "nonfat milk" are not intact, because they've been stripped of some of their dairy fat, which makes them less creamy (and caloric).
The Food and Drug Administration allows milk sellers to call different varieties of milk by a range of names. Whole milk is, for instance, also allowed to be called, simply, "milk."
Still, milk sellers have largely preferred to call and advertise milk as "whole milk," for unclear reasons.
Americans have been drinking less milk, in general, for quite some time. But it wouldn't surprise me if whole milk's precipitous fall has, at least in part, come as a result of its misleading name.