There isn't really a 'real' CB for space 4x games, besides idealogical. There isn't any issue with maps, so there no border tensions. Its cheaper to just find other places with resources then to try and militarily take it. Without the first two, you won't have a diplomatic reasons to go to war, through obligation. Even Ideological is hard to deal with, as meme to how I understand, try to propagate itself with the least amount of cost. And interstellar war is super duper expensive. Easier to colonized uncontested worlds and have the newly born population accept the meme.
As the solarian powers move away from Earth, they too are losing reasons to really go to war. Its cheaper to expand away from each other then to attack each other.
Look at the Caphilate, if they didnt decide to try and contest the Ebens from the US, they would be in an infinite stronger position then they are now, and will be more then likely forever weaker then the other solarian powers. Even if they combine with Martian Union, they're still going to be the runt.
If the game wasn't being played to help ensure conflict, the solorian powers would be better off long term, ignoring the industrialize base left on earth, making a new industrial base with new stuff. Leave earth, negate it as a security risk, negate the tension.