Because it’s a real world example. Again, answer is that flat white roofs reflect more of the visible light creating less absorption by the roof’s surface. As a result, white flat roofs radiate less heat. Here’s a good reference regarding coating parking lots with whiter coatings:
Berkeley Lab's Heat Island Group has converted a portion of a new temporary parking lot at Berkeley Lab into a cool…newscenter.lbl.gov
Note Dr. Gilbert’s comment:
“It’s amazing how hot these pavements get and how we’ve let them cover most of our urban surfaces,” said Haley Gilbert, a researcher in the Heat Island Group of Lawrence Berkeley National Laboratory (Berkeley Lab). “Because dark pavements absorb almost all of the sun’s energy, the pavement surface heats up, which in turn also warms the local air and aggravates urban heat islands.”
I will again emphasize her comment, “…Because dark pavements absorb almost all of the sun’s energy, the pavement surface heats up, ...”
I was bringing it up because I assume that almost everyone has experienced a hot parking lot or a hot roof.