Why is it wrong to join up the tops of the bar graph to make a line graph?

A line graph demonstrates the change in values across another series of values. For example the number of Apples, Oranges, and bananas sold per day for a week.

If a bar graph does not have a series of values for a single category, a line cannot be plotted. One cannot connect the tops of a bar graph showing the number of Apples, oranges, and bananas remaining at the end of the day for 1 day. The line would indicate nothing.