Why do Sinitic languages use classifiers when counting nouns?

In Sinitic languages, nouns are inherently collective in nature, functioning similarly to how the word "man" in English can signify "all human beings" rather than a single individual. Because these nouns represent an entire class, they cannot be counted or modified by demonstrative pronouns directly.12

To refer to or count a noun singly, speakers must use classifiers—a smaller set of noncollective nouns that act as intermediaries. This construction allows for specific quantification, such as "one person man" or "one animal dog," which is functionally similar to English phrases like "one head of cattle".1

It is important to note that the use of classifiers is not an original feature of the language family; it is a later development that does not belong to Proto-Sino-Tibetan and is notably absent in Tibetan.1