Avengers: Endgame was never going to have a post-credit scene according to the Joe Russo
One of the defining features of the films of the Marvel Cinematic Universe is the guaranteed presence of at least one, or more often than not, a few post-film scenes. Some of them hint at things to come, some are just a bit of fun (we're looking at you Edd The Duck). However, Avengers: Endgame bucks that trend and doesn't feature any footage once the credits start rolling.
And this was always the plan.
In an interview with USA Today, Joe Russo explained "It was called 'Endgame' for a reason. This is it. This is the ending. The book is closed on that chapter of the Marvel universe, and a new book will get written".
This is slightly at odds with Kevin Feige's earlier comments that Endgame wouldn't be the last film in 'Phase 3' - that honour will go to Spider-Man: Far From Home which will follow up on Peter Parker and Spidey in the post Endgame universe. Whether or not there'll be post credits scenes in that film remains to be seen.
Avengers: Endgame is doing huge business in the cinemas right now, breaking records globally as the biggest opening week ever and the film is expected to surpass Avatar as the highest grossing film ever.