A centralized organization (.com or .gov) that can achieve consensus amongst participants can do just fine with Postgres and a REST API.

Adversarial participants are common, but typically that's solved with a third-party overseer that administers the system. Finding use cases that demand decentralization are harder.

Bitcoin was created to remove central banks/govts from the money creation process, but in most cases, if you don't trust the central authority, you just don't participate. With cash, you can't easily get around dealing with the govt.