Uh I think you're exaggerating a bit on outstanding sales... maybe before TK happened (2003-pre); but since the game series has been lucky to break 500,000 copies, and it hasn't in 4-5 years. The reputation of Koei's games continues to plummet, while DOA continues to garner some press and butt-loads of downloads with a solid tournament scene.
Before you use another capital word on me, I know Koei bought them, and they are in charge; but how it happened and why it happened boggles my mind. It boggles my mind that such a low quality brand picked up TN... their library is full of some of the best games, and they've always deserved better.
The marketing for DOA sucks. I will not point fingers I guess, but wow... almost a year long wait for a character and DOAX3 for the east only, even though the east never gave the franchise a chance. And to tighten the noose, of course it's exclusive to PS4. I'm guessing Sony struck a deal with them since it's on the Vita as well. So I'm pretty sure any plans for it being released in the west are done.
It's great to be a Team NINJA fan this year!... My recommendation to everyone is to put your money at the tournament scene because we aren't getting jack shit.