It’s a standard, rock simple foreign internal defense (FID) mission. It’s dirt cheap, it builds international good will, and it can even help (to an extent) keep something resembling a stable government in place against psychotic rebel groups like, say, Boko Haram.
How do you know the people you are training won’t join Boko Haram or a similar group ... and now they have your training and probably military equipment?
That is what has happened numerous other places.