Why is Mario so poor and cheap?

Back before they change to the human puppets, Mario was always poor and cheap. What I don't get is that how could he be poor if he worked for Nintendo? In Jeffy's 16th Birthday, he was too cheap to buy Jeffy a big cake and a better car that he bought tiny cupcakes and a broken down car. And worse of all, he can't even pay his house payments. Working at Nintendo and making games are supposed to make him a lot of money. Why did Mario became poor despite working with Nintendo?