If you can draw well(like, if you've spent a few hundred hours trying to carefully and accurately copy stuff), it's easy to outline the major proportions of a posed character or object quickly by looking at a reference and modifying it a bit. And if you have a palette set up as well, the rendering can go really fast once you know how you're going to group up the pixels(which is a major artistic decision, since clusters of same color pixels tend to read better as shapes and textures). So the payoff for 3D tends to manifest only after you have a lot of frames to render - each frame, on its own, tends to be fast to paint.
Basically, if you look at where CG is used in contemporary anime, that's where the line is drawn. Many shows will CG their vehicle shots and parts of their action scenes since they call for a lot of perspective drawing with swooping camera movements. They may use and trace over CG dolls to do establishing shots or get static posed characters in a scene, but once detailed acting is called for they tend to revert to drawing in keyframes. Again, generally relying on reference footage to get the acting down, but modifying it to fit the character designs.
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If you can draw well(like, if you've spent a few hundred hours trying to carefully and accurately copy stuff), it's easy to outline the major proportions of a posed character or object quickly by looking at a reference and modifying it a bit. And if you have a palette set up as well, the rendering can go really fast once you know how you're going to group up the pixels(which is a major artistic decision, since clusters of same color pixels tend to read better as shapes and textures). So the payoff for 3D tends to manifest only after you have a lot of frames to render - each frame, on its own, tends to be fast to paint.
Basically, if you look at where CG is used in contemporary anime, that's where the line is drawn. Many shows will CG their vehicle shots and parts of their action scenes since they call for a lot of perspective drawing with swooping camera movements. They may use and trace over CG dolls to do establishing shots or get static posed characters in a scene, but once detailed acting is called for they tend to revert to drawing in keyframes. Again, generally relying on reference footage to get the acting down, but modifying it to fit the character designs.