Why doesn't wobbly windows in Gnome work?
Solution 1:
The wobbly windows is a feature not of Gnome, but of the window manager e.g. Compiz. The Window manager in Gnome Shell is Mutter. and this does does not support Wobbly Windows (yet). There is a Gnome Shell extension in beta that allows you to get a wobbly window effect. This appears to be buggy currently and is only a beta.
Solution 2:
Gnome Shell support wobbly windows, you can install this extension to get wobbly working.