Once upon a time there was a grandmother, who's passion in life was to tell stories. Her grandchildren would become encaptured it the beautiful tales she would weave. Soon, they invited their friends to come. And soon they invited their parents. And they began giving money to her so that she could do it more.
If she had said, "sure I have time to tell stories, but what good will that do", shed have never allowed that to happen.
That's proving his point, though. The issue is whether the grandmother feels like telling stories, not whether some of her audience members are bribing her for it. The money doesn't actually help her do it more until it lets her quit her job or the like, which isn't terribly likely in the case of running forum games for thirty people.
More specifically, forum games tend to be much smaller in effort and payout than, say, flash games or in some cases pictures, which tend to be your more traditional "I made a thing this isn't my job but give me money?" operations. If you make a flash game and then make it available to everyone, it might be played by hundreds or thousands of people, a handful of whom might feel compelled to donate money over the issue. If you make a forum game and it has eight players... I mean, I suppose one of them could give you money, but it'd be trivial and probably edging into uncomfortable "is this a bribe" territory. It's also, let's be honest, usually rewarding much less work than a proper flash game or particularly detailed image until it's been running for a while.
So... overall, paying game hosts strikes me as a bit like paying people for advice on a topic they're not professionals in; I guess there's a point where it might make sense, but usually it just seems kind of excessive and weird.
On that note, when I do want to support game hosts, I typically give them the things I assume they actually want- posts, praise, and/or participation in their thread, and occasionally fanart and the like. Much more self-contained and relevant than hurling nickels at them.