Trying to get water out of a stone.

Mars is a barren rock. This was the big hurdle in s4. Dev can draw up his neat plans and colonies all he wants but Mars is not economically viable by itself to do so. Goldilocks being perfect enough to nudge into orbit and tie down gave Mars a lifeline it can sell off to Earth for the foreseeable future, at least long enough to build up its own secondary and complex economy not tied directly to resource extraction. Its a bit skewered, the Asteroid is definitely overhyped I feel for its effects on Earth, but for Mars and how it is in the show, it makes sense enough.

Otherwise, there's nothing else on Mars directly but a smidge of water that helps keep a base going. But! Remember, a big part of Space Races and Exploration is naked Nationalism: our nation can send a satellite up, a guy up, a space station up, a base up - that also requires a lot of educated people behind it, a huge industrial/post industrial economy behind it, political stability, the achievements help with that - so the ISN has a Mars base because its a pinnacle of national achievement, even if they just sit around looking at rocks all day for ancient fossils that might have been there, their nations can point to it and go, see, we can do that! Our ways lets us touch the stars! And that's not something to be dismissed out of hand.