There is a large and thriving ecosystem of GNOME extensions that add or remove various UI elements, change their appearance or behavior in all kinds of ways, including a tiling window manager. Many Linux distributions simply shipped extensions for GNOME 3 to make things look like GNOME 2. I personally never liked the traditional desktop metaphor anyways and enjoyed customizing my desktop with different extensions.

You won't get this landscape of diversity and customization if you just iterated on GNOME 2.