A third argument is to establish a back-up system that can take over if the current payments infrastructure is disrupted. Establishing a payment system that is completely independent of the existing system would require considerable resources. And a new system would still be subject to some of the same dependencies as the current system, such as the electricity grid.
In my view, it makes more sense to spend that money on enhancing the robustness of the existing systems, e.g. in relation to cyber risks. I acknowledge that the above arguments may be valid in other countries where e.g. the payment systems are more fragmented.