Indeed it is our nature to explore our environment - but that environment is not zero-gravity, extremes (and not the bearable extremes we experience on earth) of temperatures and terrain.
Indeed, there is still a substantial area of our own planet we have yet to fully explore. Why rush off to space when we've not seen all of our own planet yet?
If people had just stayed in their own locations they would find ways to become highly advanced in regards to those locations. lIkely, it wold get to the point that if they tried exploration they would be able to benefit most anyone that happened upon their civilization, and vice versa. Think about it as you would from ancient events in Eurasia. The the chinese were only able to help Europe so well because they were isolated from them for so long, even though it did really only lead to much conflict and war, but that was only because of the Europeans greed.