"I also asked Shuttleworth why Canonical is building its own
shell rather than customizing the GNOME Shell. He says that
Canonical made an effort to participate in the GNOME Shell design
process and found that Ubuntu's vision for the future of desktop
interfaces was fundamentally different from that of the upstream
GNOME Shell developers. He says that GNOME's rejection of global
menus, for example, is one of the key philosophical differences
that would be difficult to reconcile. Canonical has accumulated a
team of professional designers with considerable expertise over the
past few years. They want to set their own direction and create a
user experience that meets the needs of their audience. The other
major Linux vendors, who are setting the direction of GNOME Shell's
design, have different priorities and are arguably less focused
than Ubuntu on serving basic desktop users.
"There are also technical issues that drove the decision.
Ubuntu's developers are deeply dissatisfied with GNOME's new Mutter
window manager, for example..."