Story is easy because the writer (or team of writers) can come in, get everything done in about 4 to 6 months of hard work, and move on. And even if it's not brilliant, the game can still do well (look at Terraria: not big on story, but quite fun to play). Compare that to art: a single artists can't practically make every bit of it that a game will need, and a team would be working on it for about a year at least (to my understanding), and they can't really start until some basic parameters are set. The game can't generally be practically programmed by a single person anymore (again, to my knowledge), that is where the most people-hours go, and if you get it even slightly wrong, the thing wont run.
The story has several difficult parts (not least of which is keeping it under control, since everyone loves story and wants to add to it), but objectively speaking, fan games tend to have plenty of story and not enough everything else.
Faust, while talents might be able to be drawn from the fan community (and some of the development would be public to that community), I'd think a business model would be the way to go. People are hired or fired from the project and so on. Honestly, if we're just relying on people's largess and free time, it wont get done.