We have a limited amount of resources.

We can spend quadrillions of dollars to set up a self-sustaining colony on the cold, dark, airless, arid, lifeless, radioactive, poisonous deserts of Mars, or for a fraction of that money, we could stabilize our biosphere here on Earth and save our ecosystem for all generations to come.

Clearly we cannot do both as we aren’t doing either one. I would add that rocketry is wildly consumptive of energy, and that energy is 80% fossil fuel generated (though the actual rockets burn carbon neutral fuel, the energy cost of making it is, heh, astronomical.)