If we're talking about well-established fiat like USD or EUR, the currencies are devaluating gradually, so the money is necessarily lost ("the hidden tax"). However, it's lost at an expected and acceptable for most people rate. There's a tiny chance of such currencies facing hyperinflation, but since it doesn't tend to happen, people don't think about it happening. With cryptos, however, one can easily lose 10% of an investment within a day or 50% of an investment within a few months. It involves way more risk than fiat, and people are not ready to be okay with high volatility.