Depends on the rich people, some rich people like to play big but some others do not like it. If there is no rich people play big amount, so who are the one who wagered such a big amount in single bet on some gambling sites? They must be rich people, poor will not able to bet big.
If I'm going to be a rich person, I'm not going to gamble anymore because it is going to give me confidence to keep on gambling and make lose all my money. Just like these days that when you have small amount of money you don't care about it even you are going to win or lose that is going to be nothing for you.