It is really a very impressive question that push us to ask our self why do we play for fun while we are using real money ? This should be discussed deeply because it seems like we are throwing our money from the window of gambling while we need to use it in a better way.
It doesn't make sense, OP were asking why we are playing for fun using money? Really?
you already said it "for fun" that is why we are risking our money on playing gambling. People have their reasons why they are playing gambling, most of us gamble because we wanted to earn more in gambling, sadly that is not how it works, though there are few individuals who plays gambling just for fun or pastime.