Because the responsibility of the courts is to deliver justice, and to be the vanguard of social evolution. If the intention of the framers (like in Canada, where women were less then men) stnads in the way of a modern interpretation of right and wrong, then the earlier interpretation is unjust. It's allowing yourself to be ruled by the least accountable group possible, the dead. Especially a most unrepresentative sample of the dead, given that the original authors of my country's constitution were largely affluent, white, heterosexual, christian men. Nothing against that segment of people, but the modern diversity of my country would be shamed by chaining ourselves to the past. The problem is, legislatures are often controlled by self-serving politicians who would sell out justice and democracy(nothign against politicians, I want to be one), or appeal to those who would keep society dead and unchanging, and so it falls to the courts to be the last resort against the tyranny of the dead and dieing.