The real problem is Ubuntu's unwillingness to move beyond brown and orange, a combination that really should've been left in the 70s. It's a shame, because really the talent is there and in fact the GTK widgets are quite nice. However when wrapped in the Ubuntu colours the effect is really underwhelming, even off-putting. It's really time to evolve
While it is true that many will add / customise my own theme, the default theme is like the image a distro shows to the world. For a distro aimed at new Linux users, a nice theme should be a priority. Nice enough that most users won't see the need to change it, and that new users don't immediately get the idea that Ubuntu lacks aesthetic taste.