In the early 20th century, people in different fields started questioning long-held truths. E.g. the group of philosophers known as the Frankfurt school developed something called critical theory, influenced by Marx’s questioning of economics. People started realizing that knowledge was subjective and reinterpreted established facts with a more sceptical mindset, in part placing more emphasis on how upbringing, that is environment and culture, influence our perspective on reality. However, the term Cultural Marxism is a more recent invention. Some people, probably coming to the debate from a variety of starting points, have banded together in reaction to this scepticism united by their opposition to what they have labelled Cultural Marxism. Judging from the list in the article on Cultural Marxism on Metapedia, they are concerned about criticism against whites, males, heterosexuals, Christians, Westerners and the nuclear family.
The people who use the term Cultural Marxism might not all be concerned with all six issues, but as any reactionary movement, they havn’t unified behind a common ideology, they only pick and choose among any research that can be utilized in their opposition. It might seem like the reactionaries should be the ones to carry a label, rather than those they have decided should be grouped together, but without a common ideology they remain reactionaries. Labelling them doesn’t work for the same reason that the label Cultural Marxism doesn’t work; “Cultural Marxists” and “anti-Cultural Marxists” are both equally ideologically heterogeneous groups.