I'm browsing the source code of windowbuilder. In the org.eclipse.wb.core plug-in, beside the src folder, there exists src-draw2d and src-gef folders which contains an identical (or at least very similar) implementation of eclipse.gef and eclipse.gef.draw2d.
Why don't they just import these plugins but do this code duplication?
If you check the source code in those directories, you will find that it is NOT draw2d or GEF, but their own implementation of the same functionality in a more simple way. For example, the GEF abstract Command class has 11 methods and two constructors, while the "new" WB abstract Command has only one method: execute.
I think they probably did this because although GEF is incredible, it is also big and complex, so they decided to re-implement a watered down version of it.