Why were three of the "Seven Great Classics" changed to "Four Great Classics" deleted?

In the past, the term "seven masterpieces" appeared in the 1930s. However, in 1952, the China Federation of Literature and Art Circles made a report on the selection criteria and results of literary masterpieces. They thought that there were some problems with the term "seven masterpieces", so they decided to simplify the seven books into four masterpieces, including "Dream of the Red Chamber","Journey to the West","Water Margins" and "Romance of the Three Kingdoms". Among them,"Dream of the Red Chamber" was thought to have been deleted due to "complicated plot, numerous characters, and beautiful language", while "Journey to the West","Water Margins", and "Romance of the Three Kingdoms" were thought to have not been deleted due to "limitations in content that could not fully reflect the social reality of the time". In fact, there were already some problems with these masterpieces at that time. For example, some contents in Journey to the West were considered to be inconsistent with Confucian morality, while some descriptions in Water Margins were considered to be too violent and negative. These problems led to a major revolution in the history of Chinese literature.