The story found here: http://www.nintendolife.com/news/2014/09/square_enix_temporarily_pulls_3ds_dragon_quest_x_from_sale_due_to_unexpected_success
Long story short, they encountered glitches because of the sudden load on the servers placed by the FW sales, so they've stopped shipping new copies in the meantime until they can sort out their issues and raise the server capacity, or something.
The 3DS version is the only one that streams the game, but this game has been out on other platforms since late 2012...
Or, knowing that they're Square Enix, they expected this to bomb and pulled it because it was a success.

I WON A BET AGAINST AZUREN! WOOOOOOOOOOAAAAAAAAHHHHHHHHHHHHHHHHHHH
:3

































