Why do 'foo bar' and 'foo > bar' have the same specificity in CSS?

I'm curious why using > or other combinators does not affect the specificity of CSS selectors, i.e. why div span (matching a span somewhere inside a div) and div > span (matching a span which is the immediate child of a div) are considered equal regarding the specificity.

I do realize that the usage of combinators is completely irrelevant for the specificity but I wonder if there's a certain reason for it.