The day after the asteroid impact that killed the dinosaurs, when everything was on fire, Earth was way more habitable than Mars. Earth has the advantage that can live on it without support, after apocalypse some survivors can continue with rocks.

Mars has the problem of being self-sufficient without Earth. In the near-term, if Earth dies, Mars dies because there is something like chips or biologics that they can’t make. If we have technology to survive on Mars or make them self-sufficient with only millions, then that can be used on Earth to maintain civilization on Earth for any disaster. The money spent on Mars colony pays for a lot of bunkers.