'The email did not specify a reason for the cancellation'.

\https://www.mediaite.com/news/just-in-biden-inaugural-parade-cancelled/

JUST IN: Biden Inaugural Parade Cancelled

On Sunday, Mediaite obtained a copy of a U.S. Army email sent to a list of military leaders notifying them that the parade was cancelled and their participation was no longer needed.

“ALCON,” the email began (an abbreviation for “all concerned”), announcing the parade cancellation shortly after 9 pm ET Saturday:

The email did not specify a reason for the cancellation. Security concerns are always a significant issue with any presidential inauguration, or, for that matter, any event where the president and vice president will be in attendance.

However, it is believed this parade was cancelled to avoid drawing large crowds amid the coronavirus pandemic.