As the London subway illustrator said, “It’s not a map, it’s a diagram.” The technique conveys fine detail in a way that feels okay to your brain.

Also, scrolling through this for the first time in a decade… all of these graphs show darkening toward the corner. Every single one of them is a shallow V. At best, one side / one face is uniformly flat. Ambient occlusion works because light really is less common in convex spaces. For any point near a wall… there’s a wall in the way. The closer you get, the more it’s in the way.

Video games exaggerate the hell out of this effect (especially from Crysis through to this 2012 article), but heightened reality is kinda their schtick. Real people’s eyes aren’t that big, either. SSAO techniques advanced soon into wider low-frequency impact. I still have some dated PDFs with smooth-shaded church interiors.