Hi,
I know probably none of us work in graphic design, but bad designs can be the result of either bad input from the non-designers or by failing to see how the designers made poor decisions.
I am sure you have seen some bad designs in your time!
Here are two quick articles to explore.
http://iase-web.org/islp/apps/gov_stats_graphing/GoodBad/GoodBadGraphs.pdf