Bjarne Stroustrup has already answered this question:
Why doesn't C++ have a GUI?
C++ has many commercial and open source GUIs (e.g. Gtkmm, SmartWin++, V C++ GUI, FLTK, and Qt). In particular, every platform vendor provides a C++ library to access their GUI. The problem is that it doesn't have a standard GUI, and that is indeed a major problem. Note that providing a GUI is both a technical and political problem. There are lots of GUIs with lots of users, and generally they wouldn't like some other GUI to be declared standard. Anyway, the standards committee do not have the resources to build a new and better GUI.