The thing is that for many people, myself included, gambling without earning anything significant, or even losing a bit of your money, is not wasting of time. We use gambling for entertainment and relaxation, not for income generation. Hence the formula: the longer you last with the money allocated for gambling the better.
It's not always like that, of course. Every gambler knows that there are times when you can't stop, and you keep betting, and you feel exhausted in the end, and some money lost on top of that, and stuff. But with those gambling for fun this happens much less often than with those playing for profit.
There is a difference between games and gambling though...
The element of potential winning a lot of money is a huge element of gambling, that is not present in games in general.
Gaming is probably even more popular than gambling, but it still generates less revenue for the companies, because a gambler can lose so much more money in the same amount of time than a gamer.
We weren't talking about gaming, though. We discuss here gambling, right? Global video game market is actually larger than gambling market, but let's drop it, because it's out of topic entirely. Let's at least stick with gambling here, ok? Speaking of which, no, it's not a valid argument that "gambler can lose so much more money in the same amount of time than a gamer". Gambler can win a lot too, right? Casinos get their revenue from the house edge, not from what this or that gambler loses.