[Discussion]

Money is also a kind of indicator of the seriousness of intentions.
It's one thing to message Stinger on ICQ and suggest playing a casual game, and another to make it a $50 bet...
In the first case, he might only agree if he has nothing else to do, but in the second, he'll probably prioritize it.
And in general, playing for money is always more serious, less risky, and more exciting.

PS
I remember when I was a kid, I used to pester my dad and uncle to play chess with me. But what's chess with a child like? You don't even need to look at their move – just play your own game. When we played for something (not a bet, but a prize, of course, in case of victory), I didn't run around or act silly; I learned. It's a pity about the time, but raising children always requires it.)
Time is money. And while time is equal for everyone, "money" means different things to different people: for some, it's a rating, for others, a trophy, for others, cash in their pocket, and for others, experience or education.