For the sake of being a pedant, your statement is incorrect: the U.S. federal fund rate was 15% in 1981, making CDs and T-bills yield 15% APY for the products bought that year. So that kind of return has a place in reality. Granted, those were different times, different economic climate and exceptional fed actions. What you probably mean is that promising anything that exceeds SOFR + say 2 percentage points has a risk premium that should be disclosed.