Because players can claim land and might not want those walls. But don't tell anyone yet!
For all we know, he has fleshed out a colonizing event already. Based on this, we can already tell that he has put a lot more effort than simply a town with NPCs. It would appear that he has, on some level, used Millenaire as a basis.
But, more on topic, I see what you mean about the smelter, Rockboy. I was merely throwing things at a wall at that point. But I do have ideas for each building's upgrades, if you want to hear them.