Earlier quoted context omitted.
Mid-November through December is a hiring no-man's land due to the accumulation of end-of-year vacations and family trips. Most of these employees have about a month and a half before the shutdown begins and they are stuck scrambling to try to find work in the new year.
Recruiters would fill that gap readily enough.
The slowdown comes from all the moving parts who need to be in place in order to facilitate the transition of an employee to an org.
Think of your average tech hire who needs to (a) go through orientation just like everyone else, and (b) is going to take a week or two just to get his work environment and credentialing set up so he can work with the servers. I'll put my experience on that side of the desk working with dozens of clients against any anecdotal one-offs who got hired late in the year.