'Avengers: Endgame' Writers Will Defend Its Running Time
BusinessInsider.com reports "Avengers: Endgame" may have a 3-hour runtime, but the screenwriters didn't think the story could be told in a shorter time span.
...if you take on this project, and you're going to try and tie up 21 proceeding movies, if you get that done in 90 minutes, you have screwed up.
Christopher Markus, screenwriter
The writers wanted to "respect and to honor everything that came before in order to bring them to an organic conclusion.