I don't know how it could have happend any other way. Canonical backed away from GNOME Shell probably because they saw what troubled direction the design was going to and couldn't get consensus to change it so fell back to Unity which re-uses some of the same technology stack but commits fewer design sins.
There was certainly a window there where GNOME2 was becoming the Linux default desktop but that seems to be all shot up now. I don't think GNOME has ever had the resources it needed, even with Canonical, to actually flesh out a stable platform and SDK that would be acceptable to J Random developer who didn't want to have to understand the implementation details of all the components that went into GNOME. There are some third-party apps which use GTK but not so many that are full GNOME apps except what ships with the OS.