Mainstream economics is centered around recommending policies that ensure bond-holders are paid. It all leads back to that. If there is too much debt destroying the underlying economy causing bond interest payers to default, lower rates. If rates go to zero, print money to pay the bondholders. If that causes inflation raise taxes and cut spending to pay the bondholders (a.k.a austerity), etc. The political economic dimension of the relationship between bondholders and the people who pay there interest is an important missing component from our understanding.