And a lot of these jobs would have been considered full-time previously, but for political reasons such as the ACA, weak unions, Congress's general hostility to labor, the workers are classified as contractors instead.
From the econ paper these numbers are based on: >Unfortunately, we cannot determine the extent to which the replacement of traditional jobs with alternative work arrangements occurred before, during or after the Great Recession, although it is likely that there were tremendous losses of traditional jobs during the recession