Its important to point out that these are not market-based auctions. The Federal Reserve regularly steps in to purchase its own bonds (in effect skewing the price of the auction). The FED currently holds ~4 trillion worth of bonds purchased in prior auctions (its not currently increasing its holdings but it is repurchasing).
https://www.federalreserve.gov/monetarypolicy/bst_recenttren...
Central bank purchasing their own bonds can act to prop up the market, but also to disrupt market forces by keeping a "thumb on the scale". While this was initially done as an attempt to stimulate the markets after the crash of 2007/2008, it was never ceased, putting the whole financial system into real jeopardy when there is another crash and central banks have used up all of their bullets. This is a financial experiment with an uncertain end. The balance sheet of the BOJ as recently passed its annual GDP.
https://www.reuters.com/article/us-japan-economy-boj/bank-of...