static methods access static member only, why?

Well, that's just common sense. Say you have three instances of Car. Each has a different color. Your static method can be called like this - Car.StaticMethod();

Now, as it's not called from one of your three instances, which of the three possibile colors for cars that exist in your system at that time should it return ? What if you have 500 cars ?

...because they (such methods)
do not have a this-context (they are quasi global)... :)

But the static functions may receive a context, for example:

/*static*/ DWORD WIANAPI CYourDlg::ThreadWorkerProc(CYourDlg* pcDlg)
{
  if (pcDlg) {
    while (pcDlg->m_bWorkerRunning /*access by received context*/) {
      ...
    }
  }
  return 0;
}