>>724867273
Two reasons:
Stop motion is cool and trendy again but it's literally a dead art, so the best you can do is approximate it with CGI.
The low framerate allows them to easily insert and integrate elements that are produced outside of the 3d animation software, like motion graphics, sfx etc. It used to be you had to do all of this in a single program in order to integrate it, and it made CGI fx very expensive. This way you can use dedicated software for different elements and they don't look out of place in motion, which is cheaper, faster and more efficient.
We're way beyond the Reboot approach where your character is a single solid 3d model with a bunch of anchor points to move. The actual 'model' is more or less a blank mannequin and every finer detail is a 2D layer overlaid cleverly to create the illusion of depth, animated separately.
