I don’t think it can ever be solved.
Take for instance Ogre3d where I am involved: I’ve totally lost count of the many GUI libraries created for that engine.
I’ve been seeing scene editors come and go. And I’ve worked on a scene editor project for a long time.
Still, people are starting scene editor projects, and canceling them almost as quickly…
Very few people contribute to any existing project.
I guess, people want to do their thing.
Which is not ideal.
But human.
I mean: since no one is getting paid for anything, people generally don’t want to be part of teams with rules, etc.
I think.
Open source moves in mysterious ways sometimes (read: all the time!). 
