"Technical drawings are line drawings because technical drawings are line drawings". If you wanted to create an example of circular logic, that would be perfect.
Technical drawings are line drawings, because that is what was easy to create and reproduce. We see the world as solid shapes, schematic representation is purely for practical purposes, there is no particular virtue in it. It's a graphical shorthand. If we have the technology to represent reality directly, normal people prefer it. Hence video recorders, Fritzing. Engineers seem to fall somewhere on the autistic spectrum, where colors, sounds and change are all unwelcome
Here is a publication of Egyptian Engineers Handbook (incorporating Pyramid Designer) circa 3026 BCE,
Ok, now I've just totally forgotten what the point was.