Why do you think the chart is inappropriate?
I think that it is because there is no exact number shown and also the percentages must probably be rounded off when it comes to complicated numbers, not showing an more precise result. Pie chart will get messed up in angle if the numbers are complicating. Furthermore, If you're drawing out the pie chart without using computer, (with pencil and protractor) it will take a longer time for you to do it than the rest of the graphs.
Why do you think the other 3 charts are appropriate?
It is because on the other 3 charts, you can actually plot the graph and although not a pin-point accuracy, it is more precise than pie charts when it comes to big numbers.