>>4143590 lb
This has to do with the changes in income distribution over the last 50 years. Inflation adjusted incomes for the majority have seen very little benefit from productivity gains over this period, which have disproportionately accrued to the top 10% of households. Housing and healthcare costs have also experienced increases greater than the general level of prices. So the answer is: the big squeeze on the 90%. More complexity exists, but this is the core reason why most live paycheck to paycheck.