Three-dimensional graphs are handled by a completely different set of code, called Mathbox; you can see its development here. Mathboxes have their own [layouts] and objects which are distinct from their 2D counterparts.
About the Project
Authoring Sandbox
Layouts
Sidebars
Graphs
Trees
3D Graphs
Styling Graph Objects
Points
Lines
Curves
Contours
Shapes and Areas
Segments and Arrows
Angles and Angle Markers
Parameters
Calculations
Dragging
Econ Schema
Supply and Demand
Consumer Optimization
Exchange