They compete for resources and mates
The is the same as to why did European societies develop different cultural traditions in different regions.
The answer is that different groups of human beings living in their own regions are going to naturally develop their own traditions, different from other groups, as well as their own languages, etc, because they are only or mostly in contact with people in their own individual groups.
Well the answer to your question would be "land restitution" to empower farm workers and reduce inequality. It is also believed to allow previous unemployed (jobless) people to participate in the economy and better the country's economic strength :)
