Why does coffee taste so bad?

From MSNBC: “Coffee prices are at their lowest level in decades. So why does so much of the coffee you buy taste so bad?”

“This year, coffee makers are increasingly substituting low-quality beans in their ground coffee for high-quality beans … In addition, the purity of the average cup of coffee — the ratio of debris like twigs and rotten beans to actual fresh beans — has shifted markedly in the unappetizing direction over the past two years.”