I think the decline is likely attributable to two factors. First, as bar passage rates decrease, the most marginal graduates--who were already the ones most likely to enter solo practice--are the ones most likely to be squeezed out. The same holds true at very small firms, 2-10 attorneys. If the graduates who'd typically fill those spots are now failing the bar exam, we'd expect the positions to decline. A nearly 60% decline in entry-level sole practitioners, and more than a 25% decline in 2-10-attorney firm hiring, is pretty sharp in just four years.
Additionally, business & industry jobs are the ones most likely to be categorized as J.D. advantage positions, and we've seen a decline in those positions generally.
On top of that, big law hiring--at firms with more than 500 attorneys--has increased 15% in four years. Given the dramatic decline in the number of graduates--12,000 fewer graduates between 2013 and 2017--things look even better. For the Class of 2013, 8.6% of graduates ended up in the biggest of law firm jobs; that figure climbed to 13.3% for the Class of 2017. Of course, big law jobs aren't everything, and there were slight declines in 101-500-attorney firms along with federal clerkships. But, the trend is a good one.
All in all, these are good signs for the market. The employment figures are not just quantitatively better; they are also qualitatively better, as more graduates are in the most coveted jobs (again, conceding that big law jobs aren't everything), and fewer are in the more marginal or least desired positions.