[a] huge reason [previous generations avoided massive public debt] is that [they] were insecure. They lived without modern medicine, without modern technology and without modern welfare states. They lived one illness, one drought and one recession away from catastrophe. They developed a moral abhorrence about things like excessive debt, which would further magnify their vulnerability.Of course, it's common sense! When people are poorer they are more risk averse.
When you look at the history of sovereign default it's clear that it is a relatively recent phenomenon, tied to, as Brooks mentions, modern medicines, technologies, and welfare programs.