I'm just guessing, but I assume that after a certain point, what you're trying to draw is so niche and/or new that no one's bothered to make decent software for it. Like, you can do a Feynman diagram quickly on a chalk board, or spend 3x as long dragging lines in Visio or something to make a diagram diagram.
Even with CAD existing, I still always sketch initial project ideas out on paper just cause it's fast and easy.
My grocery store is literally 0.7mi from my house, but there's no sidewalks along the two 6 lane roads I'd need to follow to feet there.