https://www.cnet.com/news/avengers-4-trailer-anticipation-has-you-where-marvel-wants-you/

Complicated theories about a trailer release date for the film have arisen based on past practices, planned events and possibly the waxing and waning of the moon. Expectations were high for the trailer to drop on Wednesday, Dec. 5. But on Tuesday, rumors began to spread that Marvel would wait until Friday to respect Wednesday's solemn event, the state funeral of former US president George H.W. Bush. Marvel did not respond to a request for comment on whether this supposed schedule was accurate.

Trailer watchers have been burned before. Fans hoped Wednesday, Nov. 28 would be the big day. It was almost a year after the Avengers: Infinity War trailer came out, and the film's directors, brothers Joe and Anthony Russo, were speaking that night in Hollywood at a screening of Infinity War sponsored by Collider.