From an outside perspective, universes (which include billions of galaxies) are closed environments, instantiated for some reason. (Why do I create software apps? Why do databases exist? For any number of reasons.)

The Mantle may just be the responsibility for capturing the data of each instance (universe) before the Unload method is executed (end of universe).

What if each universe is just a bit in a quantum computer, and the sum total of life simply solves some minor equation?

Or simply, as the universe crunches (or boils away to a cold nothing), life needs an exit strategy.