They get away with this due to the dificulty of storing and moving large amounts of gold. Bitcoin is much easier to move and store. There is no advantage to holding paper bitcoin vs real bitcoin, so why would you accept paper bitcoin? Some people will fall for it, but they will get rekd, just like FTX, Celcius, MtGox, etc. I'm predicting that the dollar will finally die when legacy financial institutions fail due to trying to fractional reserve Bitcoin. It will happen quickly, just like Silicone Valley Bank.