Mr. Dan O'Brien:

The purpose of this is to intervene in the market to push down interest rates that it does not control. In normal times, because the central bank basic rate is such a benchmark for every other rate, it changes and that spills down through the other rates but because the transmission mechanism is broken, it then needs to go out into these other markets to deliberately affect the rates in those other markets. Buying government bonds directly from governments would not have the same spillover effect or may not have the same spillover effect as going into the markets among private traders.