Michael Perelman wrote:  
Because the choices studied by economists are a limited set of  
choices.  
For example, people choose as consumers, but workers have no choice  
about working conditions except to exit.  
  
  
But isn't that part of what needs to be assessed?  What shapes   
choice, is there choice, what happens if we change the frame that   
determines what choices are available?  
  
And the difference with psychology is, I suppose, that economists   
treat psychology itself as a black box.  In general, economists are   
not concerned with why people make the choices they make, only what   
choices they make and, in particular, how those choices change when   
the framework within which they make those choices change (typically   
just relative prices, but more properly the whole array of factors   
that impinge on individual behavior/choice, like how property rights   
are articulated, who has property rights, contract, torts,   
perceptions of status, etc.)  
  
Fred Carstensen