I believe Suicide Squad was also a "best seller" during preorders and we all know how that game did financially. According to the website, the "best sellers" chart updates hourly and all the other games on that chart have already come out. There is a premium edition of Elden Ring that includes the base game and DLC but like half their country bought the base game last year, so there's no reason to buy a bundle that includes the base game again.
Meanwhile if you look at the big electronics retailers that Japanese buy games at, it isn't doing so hot.
- Bic Camera has the game at #5
- Yamada Denki has it at #15
- Yodobashi has it at #29
If anything, I wouldn't be surprised if Ubisoft or a bunch of fags ordered on Amazon JP, a tactic often employed by many entertainment companies to make their product look like its doing well. Amazon JP would make perfect sense to be the site to be astroturfed since Amazon is well known in the West and the site automatically translates to English for Westerners accessing the site. Meanwhile a lot of the Westerners have likely never heard of the other JP retailers.