Aside from luck, the rich have a greater staking power than the poor, the poor will want to win big with little staking power with a bigger odd which makes the gambling more risky but the rich will pick a small odd and stake a huge amount. In the end, luck also plays a better chance.
You say it all "luck also play a better chance" this is the fact, is no that rich does lose just that we poor people don't get access to them to know whether they are losing or gaining and again because they are rich and also make use of the sense than a poor person, they play with caution and Stake carefully to avoid making a big loss, and the all of it is that they don't make money through gambling rather they first of all have their own business which is the source of their wealth.
Between rich and poor their is huge differences in times of making money and also spending, rich person can be a businessman while Poor men can be a normal hustler that hardly get something to it, so when the come to stake they put little they have to get huge amounts in return which sometimes not possible and that is how the continue to lose and again the stake everything they have that why people noticed them that they lost their game because the lost everything and have nothing to show again.
Like I said before, I do not believe the Rich wins more than the Poor, or the Poor wins more than the Rich. We cannot tell, we can only consider this in terms of edge the Rich have over the Poor which is source of stable income, high stake amount, less pressure when gambling, because this is were the weaknesses of the poor show up, pushing them to gamble irresponsibly and sometime loss much whereas the Rich would always have what to fall back on when they loss much.