mikekr's attempt at an explanation is this:
(1) Let’s consider a stereotypical manufacturing situation.There is probably something to that, but that isn't the way I see it. The way I see it is that there is that post 1980, there really is no profit-driven demand for labor. The slow growth you see in employment is demand-driven. Unemployed people desperate for incomes jockeying for position, driving employment conditions gradually down, eventually finding some way back to the trough.
With 5 workers, you product 5 widgets in 8 hourswith 5 machines
If your demand is 10 widgets, then you need 10 workers and 10 machines to produce these in 8 hours.
Often these relationships are pretty clear to management.
In a service economy, things are less clear. A retail shop has certain minimum staffing (say, 1) but if business is slow there is 1 staffer, doing not much. You might cut hours, but that cuts business even more. Once business picks up, there may be excess capacity (less boring time for the 1 clerk), OR it may be a while before the shop owner figures the queues are too long and more help is needed.
Similarly in sales: commission salesmen may not really want more “help”. Having suffered through the recession, they’d like to have people lining up outside their offices.
Either way, there is a less clear relationship between the amount of revenue and the amount of labor.
(2) Let’s consider consumer credit. If you have savings, or home equity, then in bad times you can tap these. But if you were using these assets during the previous “boom”, you will find your credit restricted and so instead of there being assets/credit lines to tap, there’s both no home equity to tap and possibly restricted credit.
In short, every bit of that work, no matter what the economists' idea of "efficiency" is totally unnecessary. It is not driven by actual demand for goods and services, but by demand for employment. Because of how politics works, politicians are totally frantic to drive these numbers back up, and so help the process. But the process only makes matters worse in the long run.
Now everybody is being paid part-time wages for full-time work and half the work being done doesn't do anybody any good.
At least, I have trouble seeing it any other way. But admittedly I'm strange about this stuff.