Here is my admittedly ignorant question about this: is it possible that the institutions borrowing these funds are actually using those funds not for relatively low-risk purposes (e.g., paying taxes), but instead to trade "overnight"? Similar to how a high-net-worth individual can borrow against their assets for a very low rate and then turn around and invest those cheap-interest-rate funds into higher-return (i.e.,…
Yes. That's the purpose. You want banks repo'ing Treasuries so they don't dump them (or their mortgages) to pay taxes (or employees or creditors). Repos finance the asset side of the borrower's balance sheet. Tying fungible dollars to specific liabilities is a losing game.
And if someone wants to repo Treasuries to take a new risk position, that's fine. The cash is still injected into the money market through the acquisition of the position. That's the point of the Fed's repo operations.
Note that hedge funds aren't at the Fed's repo desks. They're at the banks'.
> this is just more QE
Repo pre-dates QE. And the Fed supporting money markets goes back to its founding purpose. QE was novel in its scale and the assets it supported, not its act per se.