Take for instance, my cousin's husband in India, who currently holds a bunch of black money in either INR or in gold, can buy stablecoins such as DAI, then park

Take for instance, my cousin's husband in India, who currently holds a bunch of black money in either INR or in gold, can buy stablecoins such as DAI, then park it in various DeFi solutions to earn a nice return on it. So not only he is gaining an exposure in Dollar instead of a highly inflationary currency like INR, he is also able to make it work instead of burying it in a bag until he needs it. Before you start with the morality of the situation, just ignore that. You wanted to see a real use case, and I am telling you about it. As it turns out, not everyone shares your moral code, or lives in the similar legal system which allows them the similar property rights. Replace that person with a Venezuelan whose currency is completely destroyed and Venezuelan Americans are trying to provide their families with money.