3D on 2D screen is all about giving brain enough depth cues. Having size diminish with depth is a big one. The 2nd biggest thing is occlusion, which is altogether skipped in these wireframe renderings. Another big one is fog, or impact of medium the light is traveling through, very easy to do for the basic effect. It's basically just fading the colors to gray when more distant from camera.

You can have a convincing 3D with just the occlusion and fog (or even just the fog), without simulating the perspective. It's just another artistic direction.