The reason WIMP interfaces have become so prevalent since their conception at Xerox PARC is that they are very good at abstracting work-spaces, documents, and their actions.
Their analogous desktop metaphor to documents as paper sheets or folders makes WIMP interfaces easy to introduce to new users.
[1] Furthermore their basic representations as rectangular regions on a 2D flat screen make them a good fit for system programmers, thus favoring the abundance of commercial widget toolkits in this style.
However, WIMP interfaces are not optimal for working with certain tasks or through input devices which differ from a mouse and keyboard.
Interfaces based on these considerations, now called "post-WIMP", have made their way to the general public in mobile and embedded applications.