> The reason why families need two incomes nowadays is that our standards for what's "needed" have grown

Nope! It happened almost instantly after Bretton Woods system collapsed. And that wasn't because our living standards changed much, it's cause practically unbounded monetary inflation was embraced as the new standard.

Instead of benefitting from the price deflation afforded by technological progress, governments decided to debase their currencies to finance their centrally planned schemes. Combined with the relatively high transaction cost of finding a new job gave us a world where wages have stagnated.