The idea behind gambling for some people are different for some they see it as fun thing why to some they see it as a quick way of making money and others see as a side hustle but the truth is however you see it, it doesn't change the fact at the end of the day your aim is to increase the money you have some to some extent the sole aim is to multiply what you have at hand.
Both the rich and the poor gamble and that's because of the different reasons maybe for fun, maybe as a side hustle and maybe for other reasons.
So you think there's no gambler that gamble for just fun not increasing the amount they have right? If so, there wouldn't have been anything as gambling for fun or entertainment.
If you tell me that some gamblers started gambling for fun maybe at some point they got carried away and started gambling for profit, then I will agree with you, first off, make your research about gambling and how it started and the reason for it before this time, then you will understand what I'm trying to say, I agree with you that individuals has their aim for gambling but you also contradicted yourself by saying they all have a sole purpose which is doubling their money.