... For Tartakovsky, the exaggerated poses are the whole point of working in animation to begin with — cartoons, he believes, should actually be cartoonish. "I took all the aesthetics I like from 2-D and applied them here," he said. "I don't want to do animation to mimic reality. I want to push reality. You want to have your own identity. ... That was super important to me. In 2-D, the way you draw defines you, but in CG the computer takes away your identity. I wanted to make sure the movie had my point of view."
Last week, a veteran Mouse House animator and I got to talking about why MoCap doesn't seem to work in a totally non-live-action format (Christmas Carol, Moms Needs Moms, etc.) His answer (slightly paraphrased):
"Audiences know how human beings move and act. When they see mocap, it always seems a little off. People accept caricatured humans and caricatured movement that animators create. But I think they have a harder time accepting motion capture. It's "almost" real, but is off by enough to make people uneasy." ...
His observations parallel what Genndy T. says up above. People embrace cartoons. But the Uncanny Valley makes audiences uneasy in a vague, creepy kind of way.