The identical reasons this informative article describes, that open world a feeling of doing what you would like, Furthermore get a thrill of traversing to a red (or usually with my case, being dead and then visiting a red).

Unfortunately the game is simply too much for my casual game style more recently, which stinks, but I probably go back to it maybe once or twice a year since I started playing. Its not the most beneficial, but at least the devs tried different things then the standard themepark.
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