Although Joe Biden and Kamala Harris have been declared the President-Elect and Vice President-Elect, Donald Trump and Mike Pence will keep their positions until January 20th, 2021. The reason for the wait to transition to a new president, or the “lame duck” period, is rooted in historical reasons that are mostly no longer as prevalent in American life.
Originally, travel was much more time consuming across the United States, so the Continental Congress left a long period of time to allow members of Congress to travel to the ceremony. Additionally, the counting of ballots took longer than it presently does due to a lack of technology, so time was given for that after Election Day.
There used to be an even longer period of time between Election Day and Inauguration Day; George Washington was inaugurated on April 30th, 1789 after being elected on December 15th. Later, the 20th Amendment that was added in 1933 moved the inauguration date to January 20th.
Some have expressed disapproval for the “lame duck” period and feel that it is unfair to the incoming president because important decisions that will impact their next four years could be made without their input. For example, in the past, the secession of southern states was after Abraham Lincoln had been elected but before he was inaugurated.
Others feel that the period between Election Day and the new president’s inauguration is necessary to work out any issues or questions about ballot counting. In this year’s presidential election, there was a record number of mail-in ballots (more than approximately 100 million) that took time to be counted and processed. There are also pending lawsuits and recounts for the 2020 presidential election results in Georgia, Pennsylvania, Arizona, Michigan, and Nevada, so those will be settled in between November 7th (when Joe Biden exceeded the 270 necessary electoral votes) and January 20th.
Because of all these factors, Inauguration Day remains January 20th. It is not impossible for this to change with an amendment similar to the 20th Amendment in 1933, but it does not currently seem to be a priority of the parties and will likely not change in the near future.