At one time, Moana was going to involve a lot of the hand-drawn crew, and a lot of the characters were going to have traditional animation underpinnings with CG overlays. (Several animators ... a couple years back ... showed me the work).
But then the picture took a turn toward CG, as Ron Clements explained to Entertainment Weekly:
... “We still love hand-drawn animation very much, but for the depth and scope of this movie when we’re dealing with mythic islands that come to life and the ocean, digital animation really seemed appropriate for this story.” ...
Pictures evolve, sometimes for years. Now Eric Goldberg is in charge of the hand-drawn animation of the big God's tattoos ... and that's most of traditional animation inside the picture.
And then of course, there are the commercial considerations. Walt Disney Animation Studios is, after all, a subsidiary of a large entertainment conglomerate that seeks to keep stockholders content.