In case anyone else is interested, there was a lawsuit surrounding the patentability of software that automated the process. Patent eligibility is a mess right now, but this invention was considered eligible for protection. https://www.nutter.com/ip-law-bulletin/mcro-v-bandai-latest-federal-circuit-section-101-decision-breathes-new-life-into-software-patents

While computers are great at "tweening" via interpolation, the resulting motion often looks too perfect, as such sometimes motion is done over the keyframes, reintroducing some slight error. This is taken to the extreme in some cases of 3D animation wherein the computer is not allowed to interpolate tweens at all, leaving only keyframes. A cool implementation of this is explained in this GDC talk: https://youtu.be/yhGjCzxJV3E