Possible reasons for waiting: Can you think of others?
1. After Dead Period. Possible announcement on 12-17.
2. After ESD. Possible announcement on 12-22.
3. Still coaching Bowl/ Playoffs Games. Possible announcement now till 1-8-2019.
4. Coaching in high school. Possible announcement is now.
5. Coaching in NFL. Possible announcement is now through playoff elimination to all the way to the Super Bowl on February the 3rd.
Most of this is not likely, but it looks like the announcement could be as early as now to as late as January the 8th. I know this is obvious, but just throwing this out there.