There are more settlements to the south because the

There are more settlements to the south because the terrain to the south is generally less rugged than the land to the north. Settlements tend to develop in areas that are more easily accessible and where it is easier to build infrastructure such as roads and buildings. The rugged terrain of the north can make it more difficult to build settlements and infrastructure, while the relatively flat terrain of the south is more conducive to human settlement. This is a common pattern of settlement in many parts of the world, where people tend to cluster in areas that are more easily accessible and habitable. The other options, such as the land to the north being more fertile, liable to flooding, or more prone to river blindness, may also affect settlement patterns to some extent, but the rugged terrain is likely the most significant factor in this case.