The system needs to be capable of processing an extremely high number of payments per day in a secure and swift manner. And this is precisely where centralised settlement infrastructures could have an advantage over decentralised settlement.
The scalability trilemma is a term used in specialist circles to refer to the idea that only two out of three attributes – scalability, decentralisation and security – can be ensured to a satisfactory degree at the same time. Well, nobody has any interest in a system which is insecure.