I've often wondered why Debian haven't stepped up their game and focus more on desktops. They could do it and do it well. Why let Ubuntu and it's offshoots get all the glory?
While Ubuntu is focused on creating the best desktop experience possible, Debian is much more concerned with choice and flexibility. The Debian Project prefers the technically excellent solution that allows maximum flexibility, even if that means it takes more work to configure an awesome desktop. While it would be really nice if the project could polish every desktop environment it provides and develop slick installation procedures for them, that is just not practical. Like most other open-source project, Debian has a limited amount of manpower. The project prefers to focus the manpower it does have on technical infrastructure rather than desktop polish.
An opinion I have heard professed by many Debian Developers is that if someone wants to package and polish a particular desktop, they can create a derivative. Derivatives are encouraged in Debian, and most technical decisions made by the project reflect that policy. Since downstreams almost never have the manpower of Debian - including Ubuntu - they are strongly encouraged to submit patches that can benefit everyone back upstream to Debian. Consequently Debian is made better by its derivatives, and each derivative benefits from the Debian Project's manpower maintaining the core packages. It is a symbiotic relationship.
Unfortunately not all derivatives have the high quality standards of Debian, but there are some that provide an excellent experience. Ubuntu has generally (although not always) provided a very polished end-user experience, but they have focused on just one desktop: originally it was GNOME and now it is Unity. Debian could provide a high level of polish if the project was willing to railroad users into a unified experience like most derivatives do (with varying levels of success), but that is not the way the project works. That is the work of derivatives, and the Debian Project is proud of that.