Leadership is one issue. Another one is that the big Linux companies (Novell and Redhat) make most of their money from the enterprise market. So there isnt significant desktop design expenditure because the revenue slice from the Linux desktop market is vanishingly small. Canonical is trying to change this.
As an aside - www.enlightenment.org is one project which has had pretty strong leadership (Raster is a great programmer and also has good aesthetic sensibilities). I hope enlightenment comes back and the big two (KDE and Gnome) becomes the big four (kde, gnome, ubuntus take on gnome and enlightenment).
The problem with the Enlightenment guys (as I understood) is that they always had big plans and awesome ideas, but there's just not many enough of them to implement everything they want.
They might consider to simply take the good parts of KDE/Gnome and build a visual shell around it to their liking. Kind of like what Canonical is doing.
As an aside - www.enlightenment.org is one project which has had pretty strong leadership (Raster is a great programmer and also has good aesthetic sensibilities). I hope enlightenment comes back and the big two (KDE and Gnome) becomes the big four (kde, gnome, ubuntus take on gnome and enlightenment).