Why are the reflectance levels for most materials set so high? Many that I have found are between 70-90%.

Other than Aluminum panels, white cement tile, or other highly reflective roofing materials I am not aware of anything that is much higher than 65-70%. Other than Fresh snow, I'm not sure why anything would have a surface reflectivity anywhere close to 90%.

There is even a warning dialog that says the Surface Relectivity is "unrealistically high". Why is this the default?