I imagine, so he can make money off it. The problem with Open Source is, as you've mentioned, that you can't "just" sell it. Open Source makes its money through "support". If someone makes a game, they will need money, to pay for the art designed, and the labor that went into the programming and design.
Don't get me wrong, Open Source is great, but it does not fit well into the current society, where you
need money to survive. In my eyes, Open Source projects have two competitive points, as where closed source only has one. With closed source software, you just need to really provide a better game to make money. With Open Source software, you need to provide a better game, for one, and to actually make money once you've attracted people, better "support". Open Source is not the way to make money in our current society, where, as I've said already, money is required to live.
It's kind of a double edged sword. You can't pay all the contributors in an Open Source project, because there are too many. Money is made through "support"... but how does that pay off the programming others have contributed? It doesn't... not really... With closed source software, you know who did what, who deserves to get paid, and they can be paid for their efforts.
Role-Playing:
Mr. Joe Someone contributed a huge bug fix, which was well needed by many people, to, lets say, the Linux Kernel. Will he get paid for his labor he put into finding the bug, and correcting it? No.
As stated earlier, if someone has to pay for a program, if it's open source, they can just go find another distribution giving it away for free. That doesn't work! Labor needs to be paid for. Nothing is free in this word. It's the very sad truth, unfortunately. Open Source doesn't pay for the labor done by people. With closed source, you can ensure that nobody is going to get your labor for free by a different distributor.
That means if the developers want to make serious money they will have to provide support and warranty themselves in their own distribution,
In addition to doing labor (programming) they are now forced to do more labor (support) just to earn money for their original labor (programming)? That is a problem. Now they must succumb to two types of labor, just to pay for the expense of the original labor...
I don't mean to argue.. but there is a reason that things are closed source and should stay that way... I'm also sorry if this doesn't make sense.. A little lack of sleep...