Captain America wasn’t exactly on the sidelines in Avengers: Infinity War, but for a character of his importance, he certainly played a smaller role. According to Infinity War and Endgame writers Christopher Markus and Stephen McFeely, this was done on purpose.
“When I was talking about [Infinity War], I very often said that sometimes we gave ourselves permission to tell more story for a character in Endgame than in Infinity War,” McFeely told Gizmodo. “Cap’s a great example. People counted Cap’s lines [in Infinity War] and he had like 20. So Cap steps forward, as you can probably tell, pretty dramatically in Endgame. And that’s because we knew some people had more interesting stories after [the Snap] than before it. Cap and Natasha are good examples of that. So I wouldn’t say we shortchange anybody [in Endgame], but part of the reason there are only  people on that poster was to go deeper with fewer.”
The duo was able to balance and plot out which stories were told in each of the movies because they developed both films simultaneously, outlined them together and wrote them back to back. They knew the ending of Endgame even before they started writing Infinity War.
“There are two movies. They’re clearly linked, but they’re meant to tell one story in two radically different parts,” McFeely said.
When asked if the still-unresolved Captain America/Tony Stark feud from Captain America: Civil War would be a part of that expanded role for Captain America, the writers remained coy.
“Hard to say,” said McFeely. “But their relationship is one we would like to see addressed.”
“They are kind of looking in the same direction on the poster,” added Markus.
(If you couldn’t tell by the two references to the Endgame poster, it was sitting next to us in our interview. Here it is, so you can see what Markus was talking about.)
The main poster for Endgame.
As the poster, which actually includes everyone but Okoyo and Thor looking the same way, states: Avengers: Endgame opens 25th April. That's tomorrow!