Can be many, if not greedy.. but can be broke all too ,but i never heard people earn money by just gambling.
But gambling gives them fun and excitement,that makes them gamble even they had no chance of winning.
Yes, there is no certain amount you can win in gambling and i think it all depends on how much money you will spend to gamble. you can earn big if you win but just a reminder not to gamble your hard earned money so it wont wreck your life.