One who wins makes more and one who loses - loses more. I am not much into gambling but yeah I played some games I can say that I saw losses more than wins.
It has nothing to do with being poor or rich, it is all about luck (IMO). The profit of rich gamblers can be seen by the poor and they get attracted to it but no one cares about the poor's loss/profit.
The gambler who had started the game with the winning will keep some bucks in the short period of time.The gambler get the losses and win in the counter cycle manner,but the survival of the game with loss will help to taste the valuable winning.For the certain period of time,you may face the loss again and again.But if the gambler learn the game tactics,it help them to get away from the losses.The rich people may not huge losses in the gambling site.Because the gamblers with huge backup money can tackle all the loses in the game and able to taste the game win for the longer term.The poor gamblers should arrange huge before the game begins.