From a General Accounting Office report referenced in the RAND Report.
Historical labor market data from 2000 through 2012 provide mixed evidence as to whether an airline pilot shortage exists. The unemployment rate for the pilot occupation—a key indicator for a shortage—has been much lower than for the economy as a whole, which is consistent with a shortage. On the other hand, wage earnings and employment were not consistent with the existence of a shortage, as data for both indicators showed decreases over the period. In looking forward, to meet the expectation of growth in the industry and to replace expected mandatory age-related pilot retirements, projections indicate the industry will need to hire a few thousand pilots on average each year over the next 10 years. Data indicate that a large pool of qualified pilots exists relative to the projected demand, but whether such pilots are willing or available to work at wages being offered is unknown (GAO 2014).
Cliff's notes: Airlines are paying less and less. Astonishingly, pilots are less willing to work for decreasing wages.