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 put up a $50 bet...
In the first case, he might only agree if he has nothing else to do, but in the second, the priority will probably increase. 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? You don't even have to look at his 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. Moreover, if time is equal for everyone, then "money" is different for everyone: for some, it's a rating, for some, it's a trophy, for some, it's money in their pocket, and for some, it's experience or education.