In some parts of the world, government is hostile towards their own population, either by incompetence or malice. Debasement of the national fiat currency is theft perpetrated by the government and crypto provides an alternative for that.
Can you just use US Dollars? Sure you can. But your government can search you for the bills. Or they can block the specific website you're using or the US banks can be hostile towards citizens of your country (Neteller, skrill and several others outright banned Venezuelan citizens, and some US banks are making difficult the process to open bank accounts)
But how about volatility? Sure is a problem. But with fiat you know is only going down, at least with crypto it can go up.
Is always interesting seeing the threads on HN on crypto and how it never considers an actual hostile government.