For anyone actually thinking of abandoning Nutaku completely for DMM, you should think through carefully your reasons.

If it's just because the Nutaku gacha hasn't been treating you kindly, that is still very much a possibility on DMM. Yes you get more freebies and thus more chances, but that doesn't increases each individual roll's chance of giving you a 5* or 6* knight. Remember that rainbows are still a 0.5% chance.
It's just the nature of gacha games like this. Players that get salty that they aren't getting the rarest characters quickly and naturally will always have that looming raincloud over them impeding their enjoyment of games like FKG. For gacha based game, it's best to appreciate what you have now rather than what you wont be getting.
New units are added every month. Eventually you'll run into more and more units you'll really want, and the cycle continues.

If it's because DMM has more content, then you're basically leaving Nutaku because you do not want to wait for it to finally get those features implemented. Which is your prerogative. I will say that Nutaku FKG has been fairly consistent with it's content updates, matching the pace of DMM's version when they were less than a year old as well. So it's not like we aren't getting those updates eventually (yet, the future is always uncertain).

These seem to be the two most common reasons I'm seeing a lot of.