I think it's about money, when there is money involved it gives you adrenaline rush, and gamblers seems to be addicted to it and they can't seem to find that feeling anywhere else.
But you can put money also while playing Online games?and remember the Competition of online gaming now has a Huge amount of money Pot so I guess OP has a point on asking this
Because in gaming we can totally enjoy to the max and can also gain winnings at the same time
I think it only basis on where are we comfortable to deal off. Most people are using online games as it is trending on social sites but I prefer to play gamble as I found it entertaining and it also a good way to release stress from work. I always look forward and not attach on every possible conclusion but taking this play for fun instead.