Until the banks (or the government, or someone more powerful than you) decides you shall not use your money and those funds get blocked. Or maybe you don't want to tell your bank, or the government, what you do with your money. Yes, there's cash, but it's going away. And please don't tell me "you have nothing to hide, so nothing to worry", there's plenty of legitimate reasons for privacy.

If people stopped thinking about crypto as "EaZZy MoNey" and instead, just treated it for what it was meant for, as a currency, it could actually be useful. But please let's get rid of proof-of-work and energy waste.