Most Xbox games don't even release physically.
Scarlet Nexus and MS Flight Simulator are some of very few physically released XBS games in Japan and neither came close to charting in the top 30. Taking this from resetera, iirc they only shipped 500 Xbox copies of Scarlet Nexus.
It's not really about the amount of Xbox consoles in Japan, how much the games can sell physically, it's more about wether any retailer is ready is ready to take the risk and order anything.







