Why Keep Old Laws on the Books?
A few months ago, I posted a defense of “cafeteria religion” on the grounds that the accumulated experience of a community does not always agree with the early versions of that experience that got into the sacred texts. In that case, why keep the laws on the books but reinterpret them instead of just dumping them? It's quite simple. Keeping the laws on the books enables rapid backtracking.
Sometimes the above-mentioned accumulated experience goes awry. For example, the story of the Exodus is obviously about the rescue of a people from the horribly unjust system of slavery. For centuries, it was reinterpreted in Judaism and Christianity to be about a special case with no lessons for any other situation. (After all, everybody knew that slavery was a necessary part of the economy.) A few centuries ago, a handful of evangelical Protestants (which is embarrassing to those of us in other religions) went for a more literal approach and declared that slavery could not be tolerated. This actually worked.
In a system with cafeteria religion, there will be occasional attempts to “turn back the clock.” When backtracking is needed, those attempts can be used to fix the system. If we simply dump apparently-obsolete laws, it will be harder to fix.