Others have pointed to the very slow development pace. I'll point out something else. When I was first starting out with desktop, Linux enlightenment 16 was one of the desktop options but apart from looking very 'different' to KDE or Gnome, it was damn difficult to get it to look anything other than default. Other desktop managers came on in leaps and bounds but enlightenment just stayed where it was and from what I can tell still is where it was. Meantime, kde and gnome have had multiple major versions and forks. These days I use either xfce or cinnamon, depending on whether hardware acceleration is available. Fundamentally I want my desktop environment to be a launcher for my applications and a way to manage my peripherals and UI preferences. I don't want to be looking at it or dealing with it or spending time thinking about it. I suspect that enough other people feel the same way