You’re right that many (most?) money market funds don’t tell you much about what they invest in. But there are some that stick to short-term Treasurys, such as American Century’s “Capital Preservation Fund”. I believe their minimum is $2500. As for why one would prefer that to an FDIC insured account: FDIC may take a long time to pay off, especially in a general banking panic. Treasury funds should not have that problem, as the Treasury could just sell debt to the Federal Reserve if they can’t find any other buyers. Of course, that would be very inflationary, but you can’t avoid that risk with any dollar-denominated debt investment.
