Two separate things happened -- The phrase "cultural marxism" became "marxist cultural analysis" over time in cultural studies, and conservative political theorists began using the term (capital-C) "Cultural Marxism" to mean something separate from "marxist cultural analysis." This paper is a good survey of how the meaning of the word has changed over time.

It's similar to the word "ebonics" which was the previous word for "AAVE" -- there is no page for "Ebonics" as it was originally used (being a synonym for AAVE) but instead its past meaning.