It’s a nice idea; perhaps something along the lines of a mix between Kerbal Space Program, SimCity, and Satisfactory. There’s a big problem for making this a practical step towards Martian colony planning, though; making a simulation game accurately reflect the real world is hard! If you’ve played any of the three games I mentioned, and have even general knowledge of the fields they simulate (rocketry and space travel, civic engineering and economic management, and manufacturing, respectively) you’ll see immediately that they misrepresent reality to a huge degree, and that as a result good ideas in the game don’t at all translate to reality. (Arguably, KSP reflects its subject matter best, but it’s still limited enough that discussion of the game often involves talking about “very Kerbal” designs that would be outright absurd as real aerospace engineering.)

Even if you can map out the elements of a Martian colony’s technological, social and economic underpinnings, having a game reflect those elements realistically is likely to take a heavy toll on its quality as a good game- simply because the world is very complex. There’s only a limited amount of complexity even the nerdiest gamer wants to deal with. If you doubt me, try playing some of the older Paragon Studios games- and even then, e.g. Victoria 2 was a downright impressionistic take on 19th century geopolitics. An accurate rendition of a 21st Martian colony would be far worse. Your player base would be limited to extremely wonky enthusiasts, and those people are likely already writing papers on the subject regardless.

Regardless of all the above I like the idea and have thought song similar lines myself in the past. But I can see why it doesn’t stand out to Musk as an important use of his time. He seems to feel someone else will come along to solve the actual colonization problem, as long as he just provides the rockets.