Taking it a bit far aren't you? This game is their job. I'm sure they enjoy it. And they probably play it til any reasonable person would be sick of it.

These guys are laying down the groundwork the modders are using. If it's so simple, why hasn't a similar game popped out of the ether whole cloth from a few hours of work from a handful of hardcore gamers?

Oh wait... because creating an engine, developing the interface, creating gigs worth of original content just MAYBE takes more time and effort than that. Trust me, these guys got a lot on their plates, the stuff the modders play with is still a small portion of the game overall.

As far as gameplay? Trust me, I'm no master game designer or something, but I could easily create a game so wickedly difficult only half a percent or less of people could beat it. So? That proves nothing, just that my thinking and problem solving work in a way only a small portion of people can get. The same applies to a lot of other people and specific interests, etc. The trick is making it engagingly challenging for a lot of players. That's not even close to easy. A hardcore gamer can easily build an unsellable game because they make it too difficult for most players.

And at any rate, the key question is, is it FUN? They've done a lot trying to give us that, and are still working hard finishing it.