It also has some kind of cutoff. After 2000ish readers, a book can't really get into the top10. It is not confirmed officially, but we (multiple other authors) are pretty much certain that there is some kind of rule present to make sure already popular works aren't hogging the spots.
(Which...
Because I never had one.
I don't need rights when I have lefts.
I will make sure to be as unhealthy as possible, so when one of you fanged creatures bites me, it will be like eating a hamburger you found under your car's seat one day!