By looking at the rest of the world? Do you think taxation directly on winnings is something unheard of?
Plenty of countries here in the European Union that will tax any winning ticket you try to cash out directly at the source, not matter, and not caring at all how much you actually lost before that.
People in the whole of Africa should start realizing that you can't demand your government to do the same thing as other nations when evading tax and paying the lowest taxes in the world is a national sport.
I think passing a law is the easy part, but enforcing it is a whole different story. IMO, the biggest issue in poorer countries is the lack of proper implementation. Sure, they can pass this law, but there’s no guarantee it’ll actually work. Gamblers will always find loopholes or ways to avoid complying while making sure they don’t get caught for tax evasion.