The answer is lack of productivity, because of unprecedented supply chain issues. Companies want to build things and sell stuff because the demand is there, so they employ people to do both. Many of those people are sitting on their hands with nothing to do, while still getting paid. That’s the very definition of negative GDP….being able to produce and sell fewer goods and services than you did previously.
That's real GDP, not nominal GDP. Also, people need to remember that a lot of not useful stuff gets included in GDP, particularly for government spending.
Econ professor told a parable about GDP to remind people that it's just a measurement tool, and that neither GDP (nor jobs) are what you should really be aiming for.
Two economists are walking down the street and there is a pile of dog ****. The first one bets the second that he won't eat the dog **** for $20k. The second one takes the bet, eats the ****, and gets $20k from teh first one. They continue walking down the street and the second economist is feeling regretful/embarrassed about eating ****, and when he sees another pile of dog ****, he sees it as a chance for revenge. So the second economist bets the first one $20k that he won't eat dog ****. So the first one takes the bet and eats the dog **** and gets his $20k back. They continue walking and they both get sick. The second economist says, "what were we thinking. We both ate ****, we both feel sick, and neither of us is any richer. It was all for nothing." But the first economist replies, "But it wasn't for nothing. We increased GDP by $40k and created two jobs."
ETA: A pretty good example of this from the pandemic is teaching. Teachers almost universally still got paid, even though students weren't learning (which is seen in test scores for students at schools that were shut down). So there was no drop in measured GDP but there was a significant drop in actual output.
