Everything is not like that now. Gambling is accessible to anyone, not for rich people to have fun. Even people with small incomes can gamble. Students can also gamble with their pocket money. The idea of gambling for fun may be too classic. Now, everyone who gambles has the ambition to win some money. At first, maybe a beginner gambler can say it for fun, but everything will change when someone accesses gambling more often.
Almost always it starts not as for entertainment, but for earnings, but later everything changes, when the player begins to understand that he cannot earn in gambling, for various reasons, but he likes to play, then he will continue, only this will change over time from playing for earnings to playing for entertainment.
In relation to the budget, this may even be unchanged, because the beginner at first does not play for big money, and later when he understands that he mostly loses more than he wins, then increasing the budget will not make sense, because for him it will mean a loss.