Senegal has one of the worlds highest fertility rates. They have a surplus of labour, and slowing desertification is a way of improving their ability to both subsist and grow their economy until they can drive wages up.

Note how the video points out how it is causing more people to have reasons to stay in villages that's otherwise get depleted of young people. If that continues, it will have a significant long term benefit for the growth of Senegals economy.