White collar work may have been phoning it in (literally and figuratively), but the drop is probably more likely due to "Labor Productivity (Output per Hour)" being measured using revenue from things like the social, entertainment, and travel industries taking a hit in customer spend (an empty restaurant has less output per hour than a busy restaurant, for example). It's not clear to me from that page/graph alone that an increase in stimulus spending is a cause, vs a correlation, for the drop.