I wonder if that is because most people do not grow up wealthy. So when they work hard for what they receive they have a harder time giving it up?
I think that most kids who grow up getting whatever they want can grow up to be fine people but it is truly the attitude of the parents that determines the attitude of the child.
I think some parents just give kids whatever they want to keep them out of their hair or they don't want to take the time to argue with them, it's just easier to give in. In this case children can get the wrong idea about getting material things. They come to see it as how one shows love, it becomes a comfort thing to them. Rather like a child who is always given edible treats when they are sad or as rewards for good behaviors. Food can become a way that they comfort themselves.
People who have been raised poor can become overly fastidious about their money. Penny pinchers even when it comes to themselves, they fear being unable to pay their bills, they make sure they always have plenty of money put away in case of famine.
Then there are those who kind of fly by the seat of their pants. When times are bountiful they are great at sharing and when times are lean they are happy to just get by.