Moreover, while some people work on the endless clones of the same thing, the completely different set of contributors is wasting their time cleaning up / fixing bugs / writing documentation for those endless clones.
Examples are: a lot of Linux distros, which are almost the same but not one of them comes even close to MacOSX as a desktop OS. Javascript frameworks which solve the same rendering problem again and again.
On the other side, there is Spacemacs, which tries to provide solid modern IDE-like experience on top of existing Emacs solution, leaving low-level stuff to emacs core team.