The "why".
It can't be answered. It's impossible to know their reason. But we can make probable guesses. Here are a few.
1. The science test.
Does their theories about their universe work? Will it pan out like they see in their nature? Testing it with a super-computer seems like a good way to get closer to the truth of their own origin. Our existence could be their 'thumbs up', that they got it right.
2. Entertainment v.1.0 (private)
If we are their entertainment, we should expect some degree of interaction with our "user". But there seems to be none.
But! The computer that contains us, could be located in the bedroom of some kid, who left it running, while in school. When he/she get's home, we might have self-destructed, or maybe we've become an intergalactic species…?
3. Entertainment v.2.0 (public)
Maybe they do interact, we just don't believe it, when people tell about the "supernatural". But to explain divinity and supernatural interaction on a global scale takes alot of descission-making. Perhaps we're some sort of advanced Reality-show…?
4. The digital guinea pig.
They could be facing a major crisis, and run many simulations simultaniously to quickly find the best solution.
It is critical to such a simulation, that people act and feel like real people, and critical not to interfeer, thus the lack of compassion or communication from their side.
Their crisis would occur in our world sooner or later.
The simulation would end when the best possible solution has been found.
Possible crisises could be global warming, a pandemic or even an alien invasion.
The simulation with the best solution (could be ours, could be another) might be allowed to continue as some sort of guide for their own future.
5. The mortal ancestor.
Tens of thousands of years from now, humanity has become androids in the attempt to defeat death. Now they want to know what they once were, and what mortal life was like.
