The key to this story is the series of favorable supply shocks that have, in my judgment, masked, for a time, the normal consequences of very tight labor markets and permitted the economy to operate beyond the point of long-run sustainable capacity without the usual inflationary consequences.
This could be accomplished directly, or through the myriad innovations to augment maturities through rollover options. The constraint on the average maturity ensures a degree of private sector “burden sharing” in times of crisis, since in the event of a crisis, the market value of longer maturities would doubtless fall sharply.