As a community, I think we need to do more encouraging people to do "pick up and fix the existing project for thing X" rather than "build a brand new project for thing X."
Right now it's much sexier to do the latter -- hey, you might have the next RubyonRails!
Hasn't it always been much sexier to invent your own thing? I agree, picking up existing projects should be encouraged. The problems with this approach are:
1. The original owner is not there to give you commit access, so you have to fork the project. This means that if the project had some number of users you cannot bring them with you. Imagine if there was a better version of Django out there, made by a group of talented hackers but you never heard about it because GitHub never told you that out of 1,500+ forks of Django one is really pretty awesome and actively developed.
2. The original owner is not there to give you access to distributing the software. This means that even if you create and maintain a fork of the original project, you now have to distribute it under a different name, once again losing popularity to the "standard" version.
Don't get me wrong, I'm not advocating that if a project is abandoned it be given to the next runner up automatically. The above issues also serve as a negative feedback loop preventing all sorts of bad software from cropping up. It just means that large projects like ImageMagick can effectively become zombies. You develop your code against them, then realize they are no good and have to re-write your code against a fork or evolution of that project.
Right now it's much sexier to do the latter -- hey, you might have the next RubyonRails!