[ tony there's no need to brag if someone already thinks you're cool!! ]

Well, why do humans do anything? They're curious, and they can explore. Or, more likely, because there are resources out there and somebody saw an opportunity. In that way, leaving Earth was probably no different than when people decided to find out what was on the other side of the ocean.

[ ryouma thinks humans are pretty neat, but he's also well aware of their nature. ]

Does that mean there's nobody in your world that remembers why everybody left?