It's the feeling of excitement, compulsive gamblers are not gambling for the money alone, they want the feeling and excitement which they feel whenever they win and whenever they lost, they have an urgency, to gamble because of the feeling that they want to fullfill.
But I am sure that many people have a different reason to play gambling because they want to make money from gambling itself. They don't know how to feel the fun thing inside the games because they only think about making money. We cannot say that they are doing the wrong way to use gambling to make money, but that is their decision.
of course we cannot judge unilaterally about their goals, gambling may not be entirely bad for making money,
because the proof is that many people get rich from gambling, whatever their purpose in gambling, is valid for them..