Another spotted trend in motion design is the usage of a remarkable thin line, used as an outline of simple shapes, and as extra decoration lines.
Sometimes the outline is a little bit shifted from its fill shape. Most of the time the design in this style contains a single stroke, non-scalable line weight.
The lines are often animated as if they are drawn: growing and then shrinking again, changing in other lines.
This single thin line usage gives the animations a clean, modest and elegant style. If used a sketchy, hand drawn like line, it creates a handicraft feeling, while using a straight vector line can suggest a more iconic, businesslike style.
Influences may come from icon systems that used already a non-scalable line weight to provide consistency.
Also you could compare this style a bit with the illustrations of modernist Charley Harper, who also used thin lines and geometric shapes. And because of these lines and shapes, in a way it also has some comparison with the ’50 style cartoon modern.