We do this probably because fiat currencies are already the staple means of exchange and every other thing is valued against it.
Bolding the word “staple”, due to its importance. In the society you're living, you pay everything with a fiat currency such as taxes, bills etc. The fact that you can buy a house with Bitcoin or stocks with gold is irrelevant. You will never think of an arbitrary number of sats to sell the house; you'll simply google the exchange rate and conclude how many bitcoins is your house valuated.
Not yet.
So, we both agree that at the moment it can't operate without fiat.
I never calculate how many USD a banana costs when I see an € price and then decide whether to buy it.
If you're living in a nation that forces you to use EUR, you have no reason to think the exchange rate of EUR/USD. If you were living in a nation that forced Bitcoin usage, you'd have also no reason to think its exchange rate in fiat.
Regarding government having to control money, that's a whole different topic, but I personally think it's robbery to just print money when you need it, and people who saved up money in the bank for years, and worked hard for it, have it simply devalued by a huge amount through your printing activity.
Why didn't they save up in a provable safe haven such as gold? It's known that fiat currencies are inflationary, the government doesn't keep it for secret. Whenever you feel your wealth is devaluated, grab the deflationary metal and sleep easy.