Because there's a sense of directionality in the term "progress": you cannot have progress without something to progress toward. One of Marx's key ideas was a b

Because there's a sense of directionality in the term "progress": you cannot have progress without something to progress toward. One of Marx's key ideas was a belief that such a direction is inherent in the course of humanity: a kind of implicit default that the terms "progress" and "progressive" could point without further qualification. In recent years, it has become apparent that either this "natural direction" doesn't exist, or it exists but is not as well-understood as we thought it was. Not only do our predictions fail as often as not, but our writers of fiction may actually have a better track record with their predictions than our scientists do. This makes a generalized sense of "progress" more or less meaningless. One can still speak of progress in particular desired directions, but the implicit default is gone.