Also, it could only really come from people who are truly passionate about the project, and have a very specific kind of personality that would drive them towards continuing development as it's own reward. This type of passion often comes from a certain kind of auteur/vision mentality. Things have to be done X kind of way for them. An open source project featuring multiple auteurs is going to collapse in on itself before it gets very far unless the people involved are very used to working with each other, or extremely willing to compromise. Politics is any set of people above the count of 1 with an opinion, and the politics an open source DF clone would involve would quickly bring about its own demise.
Remember, Goblin Camp started because its developer looked at DF, disagreed with its direction, and tried to fulfill a different vision. That already one "I cannot accept what you're doing, and so I'm going to do it differently," before the project had already started. I mean, that's how art often starts, but it's also terrible project management.
So it's not that DF is doomed, it's that the chances of anything like DF succeeding are already stacked so high in the "negative" that so far DF is the only one that's managed to survive infancy so far. And it's because Toady hasn't had to worry about conflicting with anyone else's vision, at least partially.