If you investigate his back story, who he works with, it becomes clear it's not about Mars.

His real enterprise is a massive DoD program, built off the Strategic Defense Initiative (the "real" Star Wars). Republicans have been trying to resurrect it for decades and Elon was part of it since at least 2001. The idea is to intercept ballistic missiles from space and end the threat of nuclear armegeddon. In that sense he is trying to "save humanity", but it's misguided because the project is already aggrevating China and Russia and is fundamentally destablizing to the nuclear stalemate/M.A.D.

This project, operating under the Space Development Agency and working with the Missile Defense Agency, requires Republicans to fund--Biden and most Democrats been trying to stop it. Twitter helps Musk with the elections and boosting Republican power, while currying favor from them when it comes to these contracts.

If you're interested to know more, Mike Griffin is the ringleader.. he goes way back with Elon. Read his career history:

https://en.wikipedia.org/wiki/Michael_D._Griffin#Career

Starlink is building up the basic tech for these constellations--currently just sensing ballistic missiles and hypersonics--but with Starship, putting kinetic weapons in orbit become feasible. Some good references here: https://en.wikipedia.org/wiki/Starlink#Military_capabilities

Yes military will use thing they can to theyr advantage, but acording to your logic all industries that manufacture anything of use for military is doing everything they do ONLY becaus of DoD.

In the end he didn't want to, because it probably became clear there was no money to gain.