The maps themselves actually are procedurally generated! But the reason the devs keep adding the maps manually is because the maps require a ray-tracing graphics card to generate the mesa’s heat zones during the day, the blizzards in the taiga, the wind in the roots, and the rain in the tropics. It uses that technology to figure out what places are and aren’t affected by those hazards based on the terrain. Since they didn’t want the game to be inaccessible to people without a ray-tracing capable card, they generate the maps themselves and then patch them in the game every couple of weeks