Maybe using current bestseller lists from amazon isn't a reliable way to gauge sales, if it can change so much from day to day. Sounds like it's just a snapshot at one point in time, not an average over time, and so it would shift around quite a bit.
Does amazon have cumulative stats, such as "most popular in April" or "most popular in 2018," that sort of thing? If so, that might provide more reliable info.
Yeah it has a 2018 list and God of War is the top selling game of 2018 on Amazon so far, also just for the hell of it console sales for the 2018 so far go Switch, PS4, X1S, PS4 Pro and X1X.