Fiat needs coercion/violence to survive.

Every fiat currency has laws that basically make it such that people have to use it—or else.

It’s all taxation. Don’t pay your taxes? They take your stuff, lock you in a cage, and/or shoot you. If your store your value in anything other than AUD and it appreciates, you owe income tax on it at some point. This is typically when you “realize the gain”. Although, I have heard (never confirmed) that some countries tax unrealized gains in some circumstances.