Most games are also closed systems, and conveniently grokkable systems, with enumerable search spaces. Which gives us easily produceable measures of the contraptions' abilities.
Whether this is the most effective path to understanding deeper questions about intelligence is an open question.
But I don't think it's fair to say that deeper questions and problems are being foregone simply to play games.
I think most 'games researchers' are pursuing these paths because they themselves and no one else has put forth any other suggestion that makes them think, "hmm, that's a really good idea, that seems like it might be viable and there is probably something interesting we could learn from it."
Do you have any suggestions?