The bar graphs were not designed to compare total amount of lines for each gender/age-range combination. Rather, they're meant to indicate how the percentage of lines for each gender is skewed older for male actors vs younger for female actors.
If they were to determine the length of each bar using amount of lines instead of percentage of lines, all that would be immediately clear is that females have less lines, a fact well established in the rest of the article, and the point would be lost.
If they were to determine the length of each bar using amount of lines instead of percentage of lines, all that would be immediately clear is that females have less lines, a fact well established in the rest of the article, and the point would be lost.