I don't think you can sell traditional investments like stocks in seconds unless it is within designated trading hours. Crypto you can trade 24/7, although fiat wires out to traditional bank accounts still operate within certain hours (at least in the US, maybe this is different elsewhere). I still hold a small amount of my portfolio in USD, even considering inflation, but this is because it's less volatile than crypto, and I think holding actual cash is better than holding a stablecoin.