Do you want to know why Japanese gamers usually opt for Nintendo and Playstation? Seriously want to know?
Japanese gamers typically like Japanese games the most. Now, hold that thought in mind.
Nintendo and Playstation together TYPICALLY GET ALL THE JAPANESE GAMES. Xbox does not. Xbox gets a few that are released worldwide and then a handful more that they paid for. Otherwise, pretty much all the smaller Japanese studios have long-standing partnerships with Nintendo and Sony.
So, logically speaking, keeping in mind that Japanese gamers typically like Japanese games, which brands are they more likely to buy? The two that, between them, will net 99% of Japanese games? Or the one that will see nowhere near that?
I know people like to make this as complicated as hell, that they like to bring in all kinds of conjecture and supposition, but really, this is incredibly simple.
There has just been very little reason for Japanese consumers to buy an Xbox. Period. No conjecture or supposition needed.