Bitcoin is volatile not in relation to USD, but to "real prices". USD or EUR are just more stable in relation to those, so it's convenient to measure BTC in USD

Bitcoin is volatile not in relation to USD, but to "real prices". USD or EUR are just more stable in relation to those, so it's convenient to measure BTC in USD. You can't fix the prices in BTC because you'd soon find that you are overpricing or underpricing in relation to real supply and demand of all the stuff around.