I am curious why people are using use Krita instead of Inkscape when Inkscape has native file support (import/export) for Synfig Studio? 
Hi and welcome here 
Krita and Inkscape are from two different worlds:
- Krita is bitmap
- Inkscape is vectorial
Synfig in its philosophy is vectorial.
But with the time, bitmap functionalities have been implemented.
Inkscape is close to Synfig in matter of drawing, with better ergonomy, but Synfig doesn’t work totally perfectly with SVG, that’s the reason a bridge has been implemented.
Why not to do the same with Krita ?
Because it is not needed 
As long as you keep to bitmap but if you keep to vector and try and import a SVG then it may not go as smoothly as the png.
You can mix both bitmaps (= png) and vectorials in Synfig.
You don’t need to vectorize any bitmap and you can animate with Skeleton either as
Cutout (youtu.be/g5VdKNL6CA8)
or
Deformation (youtu.be/s6mhTw87kMM)
As well as in Krita.