The Wall Street Journal had a bizarre article about capital investment and robotics to explain the slow job growth in this recovery. There actually is a much simpler explanation, it's called "slow growth."
Productivity growth has averaged close to 2.5 percent since 1995. That means the economy must grow at a 2.5 percent rate just to keep labor demand constant. If it grows slower than this, we expect the demand for labor to fall and the number of jobs to decrease or the average number of hours worked to fall.
Since the recovery began in the summer of 2009 GDP growth has averaged just under 2.5 percent. These means that we should not have expected the economy to create any jobs over this period. In fact, it has added almost 1,500,000. Insofar as there is a mystery, given the weak growth of the economy over the last two and a half years, it is why the economy added so many jobs.