Blockchains are useful because centralized systems cannot be trusted. They are not reliable in the long run - Especially when they keep track of something valuable like currency. Centralized systems which hold things of value attract bad actors...It's difficult to overstate how much of a problem this is. It's only a matter of time before a centralized system becomes corrupted... The more valuable it is, the sooner it will happen. The odds that the global fiat monetary/banking system has been corrupted in some major way is very high - There are just too many points of failure... Every bank can print money... There are thousands of banks in every country... The auditing of private banks can easily be gamed because centralized systems can just make up numbers... If an auditor audits a bank by querying that bank's database, how do they know that the numbers reported by the database are accurate? Auditors have to trust the centralized systems; they can't verify that what the system is reporting is true.