What's "Modern" in a Modern Recession?

Robert E. Hall of Stanford has written "How Much Do We Understand about the Modern
Recession?" which identifies some interesting facts about modern recessions:

• A modern recession is one occurring in an economy with well-executed monetary policy and a low fraction of the labor force on the factory floor. ...
• The first important fact is that modern recessions are about as severe in terms of employment as earlier ones, leaving aside the Great Depression. ...
  
• The second important fact is that the decline in employment and rise in unemployment during a modern recession occurs without any important increase in job loss. ...
• ... third important fact: unemployment rises in a modern recession because new jobs are hard to find, not because workers have lost jobs. ...
  
• One of the most important facts about the modern recession is at all sectors of the labor market slacken at the same time.
• If unemployment in a recession were the natural, efficient result of reallocation of workers from shrinking to growing sectors, the growing sectors would open their doors wide to absorb the flow of workers leaving the shrinking sectors. Vacancies would be high in the growing sectors and low in the shrinking ones. The facts shown in Figure 6 refute that view of the most recent recession. Some force made all sectors cut back their recruiting.
• What exogenous forces cause recessions? Three forces are prominent in the accounts of the various schools of macroeconomic thought: productivity, government purchases, and monetary shocks.
• The two modern recessions occurred in the setting of fully modern monetary policy making. In that setting, the central bank responds to outside influences, with the objective of keeping inflation low in the longer run and offsetting booms and recessions in the shorter run. The central bank is not a source of disturbances to the economy.

The heart of the paper discusses esoterica of Nash equilibria and why theory of wages, productivity, and employment levels don't fit the facts. I appreciated the honesty: "We have no idea how to generate a modern recession from the MP model."

Overall the paper is interesting, but you don't walk away feeling satisfied. OK, a modern recession is different, but why do we still have them? It just isn't clear. In my ignorance, I still like the old theory of "animal spirits".