It's been how long now and they still can't make a dent on the desktop. Same with macosx.
It's all about the programs it can run, no end user cares about the operating system, they care about what programs they can run on it. An operating system alone is not useful. This is why OSX does have at least some share of the desktop market, because there are quite a few popular professional-grade programs that run on it like Logic, Final Cut, Adobe Creative Suite, etc. so there are a group of professionals that can get their work done on a Mac. The choice of operating systems comes after the choice of programs for the task you want to accomplish. For example if you need Photoshop your options are Windows or OSX but not Linux or if you need Solidworks your only option is Windows, not OSX or Linux.
Linux as a desktop operating system in general has been perfectly fine for many years, but it doesn't have the application support that end users need which makes it pretty useless for most people.