Why develop rural Africa?

Northern Zambia doesn’t have a lot of people. The towns are small, and few and far in between. The land is not good for farming, in general, either. Nevertheless, foreign aid donors are spending lots of money in trying to “develop” the region. One thought that crossed my mind while I was there last week was whether this is a good use of resources. Like the rest of Africa, Zambia has been urbanizing rapidly and I doubt that there will be many people left in rural parts of northern Zambia in 20 or 30 years. So why are donors spending money there? At best, it is simply slowing urbanization. Wouldn’t it be more reasonable to accept the inevitable and pull aid from parts of Africa where people are leaving and putting more into where they are going?