The current liquidity level in the bond market is unique.
The flow of money seeking a higher current return has narrowed the spreads at which corporate debt trades over government borrowing benchmarks. This has made it possible for companies with marginal credit ratings to both refinance and raise new money on very attractive terms.
Any major jolt that hits the markets, however, could undo the base for the substantial investor leverage that has made its way into them.... Central banks are watching this carefully but might not be able to control it.
Dan Fuss FT 27 April 2021
US government debt is a safe haven the way Pearl Harbor was a safe haven in 1941.
Niall Ferguson, FT February 10 2010