Sudan is a country that has significant freshwater (the Nile), arable land and cheap labour, strategically positioned between the Arab world (which is poor in all three) and sub-Saharan Africa. Controlling those resources could be had by diplomacy and trade, or you could just arm up militias and take full advantage of the chaos. It seems like the UAE are probably using it as a proxy war to secure those assets.

Substantial gold reserves don't hurt either....