Willingness to pay the Fed tax

The remits to Treasury are a tax on the bond industry. Te tax is approximated by the difference in the two lines at the current interest rate.

The tax drops when market  rates drop but increases when the Fed buys a market rate.

The tax ultimately falls on credit banks since they have to buy bonds as collateral. It is a feed back mechanism, negative and spirals. The Fed discovers that current rates are much lower today then they were for the prior debt, which i s still clocking in at more than 2%. So the Fed taxes the bond industry for charges the US government too much in the past. This miscue, "rates are low" delusion has bit us in the ass for 20 years.

The Fed will ultimately collect enough taxes to neutralize the bad debt of the past when rate were supposedly low. Bonds holders  will begin selling on the run, counteracting the tax a bit but raising rates today. It is a balance to keep the spiral in check.