Why can't I see rows and columns within tables in the visual editor? Is there a way of turning this feature on and off or doesn't it exist at all?

We use a control written by Microsoft for the Visual Editor. Recently they removed that support from the control so that ability is no longer available. I honestly don't see if there will ever by such a feature found in the program again. What you would need to do is use the Code Editor along with Split Screen Preview instead.