Most of the jobs lost during the Great Recession paid relatively decent wages. Most of the jobs added since then pay low wages.
From a report by the National Employment Law Project:
We find that three low-wage industries (food services, retail, and employment services) added 1.7 million jobs over the past two years, fully 43 percent of net employment growth. At the same time, better-paying industries (like construction; manufacturing; finance, insurance and real estate; and information) did not grow, or did not grow enough to make up for recession losses. Other better-paying industries (like professional and technical services) saw solid growth, but not in their mid-wage occupations. And steep cuts in state and local government have hit mid- and higher-wage occupations the hardest.