If you're talking about forks, they're pretty much the complete opposite of abandonment. Forks exist because people want to work on the code.
X11 gave us XFree86, because changes to the X386 server weren't being merged. There wasn't much of an alternative to forking.
Xorg was forked from XFree86 over a license change, but after the fork, XFree86 died -- its maintainers were unable or unwilling to merge changes or do releases.