The aspiration is to represent structure in the most elemental form. Some definitions of the word "primitive" refer to a time before words existed. Shapes, motion, and relative positioning are the modes of communicating ideas and knowledge.

Also as mentioned in another comment, primitive types in programming languages lend themselves nicely to visual representation.

Hope you have a chance to try!

VR for apes.

https://www.youtube.com/watch?v=9yD4KQGZUs4

Probably a reference to primitive types, which are highlighted / represented differently in many IDEs.