Most people went to see Avatar in 3D which means tickets were way more expensive, boosting the box office. Plus it was a technological breakthrough in movie making. It's just a really bad movie plot wise. Pocahontas in space. Marvel made cinematic history plot wise. 11 years of plot writing and character building. Everyone had to see Avengers immediately because it was so spoiler full and people didn't want to have the experience ruined for them. I think Endgame is the better movie and deserves the sucsses more.