WM_CREATE is only ever sent to the window once. It is sent during the call of CreateWindowEx. So it is natural that anything drawn in WM_CREATE will only be drawn once.
The normal way of drawing to the window is done by handling the WM_PAINT message. This message is sent whenever the Window needs to be drawn. It is rare that a Windows application will not draw in the WM_PAINT handler, games tend to be the biggest application type that draws independently of the windows messages.