There is still a stigma attached to CGI or 3D imagery in anime. Because even now, it still doesn't quite measure up to the gracefulness and emotion of 2D or hand-drawn animation. Even for the most popular anime like Attack on Titan, CGI sticks out like a sore thumb. That's why some anime prefer only one way or the other. And just as there are 2D-only anime, there are also 3D-only titles (or mostly 3D).