My bet is that DMM decided to shell itself just in case. They are fine with Japan's playerbase, so they decided to "protect" them like a paranoid mother at the expense of the rest of the globe, since it doesn't give them money.
I think that due to "exclusivities" not being hard to eliminate. It's just as easy as releasing Nutaku's version in DMM too. And not giving Nutaku developing rights and using them as a tool to do " worlwide popularity pools" or whatever with DMM supervision would allow no discrepances. With a little will and coordination from both companies, there would be absolutely no problem to do so.
So, they probably decided to hide the fact than any version other than DMM's exists, so their playerbase doesn't go to Butaku's version to fool aroun and potentially spend money they would have spent on their site otherwise. That's my guess, since it's the only thing they can't avoid, as the people would wonder where did those brides come from. A bit childish fear in my opinion, since they would need to change their japanese IPs to non japanese ones to play it in Nutaku. That, and having to synchronice with Nutaku so noone releases them early.
Either that, or Nutaku negotiated trying to have exclusives. While i think the right way to negotiate would be, Nutaku is able to offer the same kind of events as DMM version, consequences included so the player experience is the same, and DMM in exchange would get free units and DMM would always have all of the Nutaku's content + more as new content generated here would be released there.
Anyway, we will never know the truth. Nor how did they negotiate, nor why did they backpedaled so suddenly (sound like a higher-up saying nope when he got the new, comapanies don't backpedal so easily without the bosses getting involved, bosses be bosses ._.)