Because macroeconomists have messed it up for every one else , says Noah Smith at The Week:
To put it mildly, economists have fallen out of favor with the public since 2008. First they failed to predict the crisis, or even to acknowledge that such crises were possible. Then they failed to agree on a solution to the recession, leaving us floundering. No wonder there has been a steady flow of anti-economics articles (for example, this, this, and this). The rakes and pitchforks are out, and the mob is ready to assault the mansion of these social-science Frankensteins.
But before you start throwing the torches, there is something I must tell you: The people you are mad at are only a small fraction of the economics profession. When people in the media say “economists,” what they usually mean is “macroeconomists.” Macroeconomists are the economists whose job is to study business cycles — booms and busts, unemployment, etc. “Macro,” as we know it in the profession, is sort of the glamor division of econ — everyone wants to know whether the economy is going to do well or poorly. Macro was what Keynes wrote about, as did Milton Friedman and Friedrich Hayek.
The problem is that it’s hard to get any usable results from macroeconomics. You can’t put the macroeconomy in a laboratory and test it. You can’t go back and run history again. You can try to compare different countries, but there are so many differences that it’s hard to know which one matters. Because it’s so hard to test out their theories, macroeconomists usually end up arguing back and forth and never reaching agreement.
Meanwhile, there are many other branches of economics, doing many vital things.
What are those vital things? Some economists find ways to improve social policies that help the unemployed, disabled, and other vulnerable populations. Others design auctions for Google. Some evaluate development polices for Kenya. Others help start-ups. And on and on. Love it or hate it, their work should be judged on its own merits, not lumped in with the very different world of macroeconomics.