I will be a big liar if I say winning money is not among the reasons why I gamble; other reasons, like using it to pass time, might follow, but one thing that fuels using gambling as a means to pass time is that there is a little possibility that I can win money out of it. If what I just want to do is entertain myself, I will use online games or involve myself in other recreational activities.
I guess that's the major reason of most gamblers and is no surprise as that is really the main goal of most. Of course, when you bet, you wish that your bet will win. Who wouldn't want such profits?