Cultural Marxism applies modes of analysis developed within the Marxist community with different presumed central conflicts than the economic class one addressed in Marxism (and a number of the early practitioners were former Marxists.) So there originally was an understandable genesis of the term.

Nowadays, it's sort of a generic derogatory epithet by the right for anything that they disagree with that can't be ascribed directly (even in a very loose view) to actual economic Marxism, because everything bad must have “Marxism” stamped on it somewhere.