It appears that the additional income coming into the household largely went into the existing costs that the household already had. For instance, shelter. If e

It appears that the additional income coming into the household largely went into the existing costs that the household already had. For instance, shelter. If every home only has one earner, shelter costs can only rise to the maximum a single earner can pay. But once households started having two incomes, the the second income helped place higher bids on securing a place to live and eventually you get to the point where you cannot live somewhere without having two incomes. In some cities today, we are reaching the point where you need three incomes (see: the robot).