Everything that Elon does on Earth is to fund and build his Mars colony. Rockets, solar, tunnels, satellites. Now he's getting into social. How will future martians to communicate with each other? (And importantly, how to do politics..?)

All his ventures start out with him trying to other systems first. (He started SpaceX because it was easier than buying a Russian ICBM).

He would build his own social media company if he could -- however, the most valuable thing that Twitter has is the network. Everyone is on Twitter. That alone is worth the purchase. I would not be surprised if he plans to redesign the whole website starting from scratch.