Let’s assume that a bad chart is a chart that breaks basic perceptual laws, contains too much fluff, do not respect data relationships and do not clearly answer the underlying question (if you can find one). Why do people make such charts? Below you can find some reasons. Check the ones you agree with. You can select as many as you wish, but do try to choose the more relevant ones.
Thanks for your answers. If there are reasons lot listed above please discuss them in the comments.