Why Govt. does retrospective amendment in tax laws?

To win pending cases of tax laws. Indian Govt. has carried out retrospective amendment in tax laws from very inception of tax laws i.e. 1962. The retrospective amendment should be carried out when the cases are pending in Courts. When assessee takes advantages of loopholes in tax laws and win the cases in lower courts then the Govt. files the cases in higer courts and to win those cases makes retrospective amendments.