But I think it would be more beneficial to discuss ways to increase activity on the forums rather than being bummed out about it.
A community game project could be interesting. Something "simple" and doable with low production value. And actually put it together not just mockup.
The game could be very loose. No need to put your million dollar ideas and art into it.
We could ignore style matching so that more people would get involved. I've always thought that WarioWare looked nice despite having lots of different styles and mediums of art mixed together. although each game feels coherent within itself compared to all the other games there is a large variety.
Another way to go would be set a very simple style. but that might not appeal to everyone.
Personally I'm not so strict with matching drawing types. Cute things can exist among violent things or vice versa. Just using pallets and number of lighting passes ties things together well enough.
The SMB1 topic seemed to generate a lot of conversation. But the game was Arne's alone. And sometimes its better to do a game by yourself or with a very small team. But It'd be interesting to lump together a game with lots of people. If every post in that topic said "hey this is what I made for the game" and attached something a lot of work would have been generated.
The challenges I foresee in random order:
1. Common Interest - not everyone has the same taste in games and art
2. Huge list of features - everyone will want to provide their own ideas. not a bad thing but good code takes time like anything else
3. Ownership - If I move to Kenya and sell for millions how will you find and sue me? or anyone else?
4. PipeLining - This is always a challenge. organization and communication.
5. Documentation - Google.docs is great for summarizing a game and listing tasks but who will have rights to edit? everyone? one guy? select few?
6. Foresight - like most things game projects need positive mentality. if that is lost the project is prone to die.
I can volunteer some game programming. Currently I have quite a bit of studying to do. Development would go a little slow. Making a "simple" game is still quite a bit of work.
It's just an idea. I'd hate to rob people of time. I'm extremely busy myself. And I understand why most people don't want to hand out free art. Its very time consuming and mentally expensive to produce. I understand if people have more important things to do like make money and eat food.