Shenmue 3 has had a lot of controversy leading up to its release but the low sales numbers may have nothing to do with it. However, it is quite odd that the game couldn't outsell even the remasters of the first two games with a poor opening.
Ys Net ran into trouble with Shenmue 3 backers when they announced the game would be exclusive on Epic Games Store, with the latter cleaning up the mess as they covered the refund costs.
While one could be led to believe such a mess would reflect on the game sales, it's possible they wouldn't be wrong but it's also true that the fiasco had nothing to do with poor opening sales in Japan. This is due to Game Data Library's metrics collecting info only from PlayStation 4 sales and comparing them only to sales from past years, on respective consoles alone.
Therefore, the PS4 sales of Shenmue 3 were compared to Shenmue 1 and 2 sales on Dreamcast as well as remasters' opening sales on PS4. Shenmue 1's opening sales included the first two weeks of launch while only the first week was taken into account for the rest.
It's safe to say that the first two games sold like hotcakes in Japan, with the original gathering 257,775 copies sold across two weeks and the sequel 92,917 over the first week.
The remasters of the first two games arrived almost two decades later, in 2018, when they sold 19,701 copies in the first week. Shenmue 3 did not manage to beat even that number, with just 17,857 copies sold.
It is unclear whether the sales included copies granted through crowdfunding but even then the sales would not look too impressive, only managing to outsell the remasters in the initial stretch. Then again, Shenmue 3 is a sequel to a game that came out 18 years ago and the main appeal was for the long-running fans of the series.