Ask HN: Why there is a huge diff. in no.of cookies in gmail & Facebook?

Got a question for HN readers. I recently installed a extension Vanilla Cookie Manager on my chrome. It tracks the number of cookies downloaded when you visit any site. I noticed when I visit gmail(just log in & log out) its shows number of cookies as 165. When I do the same with my facebook account there the count is only 12. Why this huge discrepancy? Can somebody throw light on this.