Desperation to win can make you fall for anything but i am sure that it has nothing to do with voodoo or black magic but rather its a matter of chance.
Desperate times call for desperate measures. I guess someone experienced some hardship or losses that lead them to think that a voodoo doll or something would help them to win in gambling by any means. Chances are still the same even if there's no voodoo and charms but if it is a skill-based game, chances of winning would depend on them.