https://www.techspot.com/news/77538-call-duty-black-ops-4-best-selling-game.html
 
The latest installment in the Call of Duty franchise, Black Ops 4, is the best selling videogame of 2018, according to the NPD Group. This is the first Call of Duty game to favor of a no-holds-barred multiplayer mode, thus betting in replayability and user interaction instead of on the ages-old single-player immersion. The decision to cut-back in single-player development efforts, time, and funding apparently didn't hurt Call of Duty: Black Ops 4's market penetration, but not all is lost in the single-player world: Red Dead Redemption 2 has been on the market for 14 less days than Call of Duty, and has achieved best-selling title for October - and the second-most sold game of 2018. Based on feedback that I've personally heard the game seems worthy of the franchise.

The game really is not very good. I played a few hours here and there and then forgot about it when Battlefield 5 came out. 

Really not that surprised because it's on everything. Red Dead 2 is probably the better game but you have to have a PS4 or Xbox to run it. Other games I could see for best seller this year would be Farcry 5 which has been out almost all year as well as God of War for the PS4 as well as Spiderman. Both has been very well reviewed games. I am also surprised that we are not seeing World of Warcraft Battle for Azeroth as the best seller since normally expansions get people to come back to WoW.