It continues because it's becoming an African euro-zone, having the same currency is invaluable. Especially that the African currencies don't have a reputation for stability. It's not a coincidence Mali & Guinea left and then came back in.
> Lastly, one just has to compare the state of Francophone African states towards most of the Anglo states, they are on by definition normally poorer and more fragile
I don't really agree with that, you have counter example in both cases, on my case I could point Cote d'Ivoire where the Bank of Africa is located and on the other Anglo side you have Uganda which isn't exactly an example of a rich country, the Franc CFA definitely helped for that.