Why are politicians such poor money managers of their nations econoomies?

They are poor money mangers because:
     1.     the system in certain countries operates by corruption
     2.     the system in certain countries operates by covert                              corruption
     3.     the system's raison detre is to ensure the rich, the powerful 
              and the good become even richer, more powerful and 
              gooder
      4.     the system's system raison detre is to pour money upon 
              their sans culottes so that they remain beholden to them
              and remember to vote them in again.

In one way or another politicians do not seek power to ensure and to sustain the common good. 
They are all self-serving ladies and gentlemen.