This is by way of holding up a mirror to the community of users. Also, sessions are not visitors but visits.
Many folks come several times a month.
Each time you view a page, you actually generate many hits, on the order of 10 hits per page. A page view is one page. One session is counted each time one user views a number of pages then exits. It is an imprecise measure as identifying and tracking a single user is not a precise matter. But clearly there is a lot of interest in the subject matter of this site out there.