>* the widening gap between productivity and employment in America... is deeply troubling to economists. But it’s possible... that the gap could contain all these people we are currently not counting.*

Growing productivity could also just lead to decreasing employment if the same roles are being accomplished by fewer people who do them more efficiently. Having a bit of work on the side essentially amounts to people who are employed doing more, rather than unemployed people having an Etsy or ebay shop which is their main employment. And many of these people probably don't count as "unemployed," as there are advantages to being set up as a full time seller (at least on ebay and amazon) for tax purposes.