Someone who creates these renderings for a living could describe this better, but the exaggerated angles of the upper floors has something to do with the sides of the buildings remaining vertical in the renderings. While in reality we would see the buildings narrow as the tops recede into the distance from our viewpoint, marketers don't want the tops of buildings to appear small, or for the details to disappear. It all makes for a slightly strange effect, but one that I get the feeling that it is not going to go away anytime soon!
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