The only reason to buy 0% interest Treasury Bills, or worse negative interest rate bills, would be because you think the alternatives are even worse. I can understand the Treasury Bills being seen as a safe harbor against an expected stock market collapse, but as low as the interest rates may be, putting money into Federally insured bank accounts ($250K individual, $500K on joint accounts) will earn you something, especially if you go with longer term CD’s. If you trust the govt to pay you back on the Treasury Bills you can trust them to make good on the federal deposit insurance should the bank fail. My guess is that it isn’t individual investors buying the 0% interest Treasury Bills however but rather institutional investors with amounts that normal bank accounts just don’t work for. Even for mega wealthy individuals, trying to put it in $250,000 or $500,000 chunks in individual banks is not practical due to how many banks they’d need to deal with.