Why life expectance is growing faster than retirement age? - source needed
Loss-aversion and political tactics.

A lot of the elderly are no longer physical broke down - which was the original reason for retirement. But, if you can retire in good health, it is completely rational for the individual to do this, and to vote for the politicians who will provide this for you. 

Or, as a danish mayor once put it: 


  "When you first throw something into the monky cage, it is hard to
  get it back again"


Aka, when you first give people major entitlements and life improvements, it is next to political impossible to take them away.