I really don't know.
1) The Fed was created as an independent bank, which prevents some politician from changing interest rates to appease the people (e.g., everyone would initially love a president who changed the interest rate to negative 20% or positive 20% or whatever, until the banks collapsed, and no one could buy gasoline). The Fed determines some central interest rates. Those interest rates are usually substantially lower than most commercial rates (e.g., commercial loans used to sit at like 9%, mortgage rates sat around 4%, and federal rates were around 1%).
2) The Department of the Treasury is where your IRS payments go. The Treasury lends money to people based upon the Federal Reserve interest rates. Everyone likes to lend money to the Treasury, even if it pays less than elsewhere, because the loans are guaranteed by the US Government (i.e., the USA would have to go under before the lender would be screwed). Short term loans to the Treasury are called T bills. Longer term loans are called t-notes. By issuing these loans, the Treasury ensures that interests rates are fairly for the foreseeable future (e.g., the federal government believes that the interest rates will be X in The next 6 months). Because foreign entities can lend money to the Treasury Department, the value of their money becomes tied to the USD, and we get some international monetary stability (e.g., if China has lent $20 billion yuan to the Treasury, then China's economy is mildly dependent on US interest rates).
3) You know how idiots talk about "the national debt" as if it is credit card loans? Approximately $29 trillion dollars of that debt are loans from the treasury department. Think about what would happen if Visa told everyone, “we don’t let anyone carry a balance, pay up, and ….”? End of business for Visa, most retail places go juts, most wholesale places lose it, etc. now go national, and think about what would happen if the Treasury told everyone, "we are no longer borrowing money. Here's your money, go away"?. Now no one wants to lend the US money, interests rates become unstable, the USD would become less stable, and we have all sorts of problems.
4) Federal student loan interest rates are Congressionally required to be a percentage of current T-note/bill rates (i.e., if the T bill pays 4%, then federal student loans must charge 7% to make sure they don't lose money). Federal student loans are also not discharge-able by bankruptcy, or other difficulties. Until 2018, disability didn't even stop your student loans obligation. It’s a way to lend money at a higher rate, get payment on that higher rate, and then lend those payments out at lower rate, etc.
5) The last published figure for the total value of federal student loan obligation was about $3 trillion.
6) The last published figure for the total value of T-bills, T-notes, and treasury bonds was about $29 Trillion.
7) The BBB says, “forget about lending money out at higher rates, which we could use to lend out at lower rates. While we are legally required to lend money out at one rate, we don’t want to lend money out at a higher rate, and us that to make money.”
