>and the ruling directs how the government implements the law for the next 50 years.

The legislature and executive could pass a new law the same day as the ruling (well, maybe not if the new law required a constitutional amendment) if they really needed to and there was sufficient political will. In practice what you see is that the judicial branch only weighs in on controversial issues where there tends to be a pretty even split so it takes a long time for things to change enough for side to build the political will to get law passed to overturn the judicial precedent.