The IRS shuts down all their computer systems for a long window around the holiday season as they transition from one tax year to the next; if you need help from the IRS in this time frame they just can't do it for this reason.

It's not just that. If you need to use their court system they shut that down part of the year too which can lead to additional penalties if trying to fight an incorrect late penalty. Their legal system is entirely isolated from the federal courts.