Physical money has value because we have an economy. If you have a USD, you can come to the US and spend that dollar. Bitcoin doesn't have an economy, it is literally a meme. The only thing you can do with it is trade it for real money.
The value of USD is based on the US economy. The value of Bitcoin is based on people's perception of the value of Bitcoin.
If all programmers decide to be paid in crypto, and you need a programmer, the crypto has the same value as USD ("backed by programmers")
If everyone in your economy decides to be paid in crypto, USD will find itself in a very bad position.
Your economy is now driven by USD, but it's not a law in any way.
“The value of USD is based on US economy” but far from being an expert I suspect that what is behind at then is human perception and trust, you can choose to keep the token USD or token Bitcoin depending what you perceive as being safer or trustworthy, and some people prefer to have eggs in both baskets.
The value of USD is based on the US economy. The value of Bitcoin is based on people's perception of the value of Bitcoin.