Most distributions of Linux are not designed for a superior desktop experience. This even extends to the way programs are installed. Windows and Mac OS users are familiar with the idea of downloading an application and installing it by clicking a file. Linux itself - without the help of WINE - does not recognize an .exe extension, and this causes a problem.
Most applications are installed in Linux with the help of a graphical Package Manager. It hides some complexity from the user, but it doesn’t hide the fact that a single, simple application may require that several other “packages” also be downloaded and installed in order for the application to run. This interdependency of applications and complexity is strange to a Windows or Mac user who expects her applications to just install and work all by themselves.