The screenwriters for six films in the Marvel Cinematic Universe, including Avengers: Endgame, Christopher Markus and Stephen McFeely, shared in an interview with The New York Times as to why they didn’t include certain characters in the final film.
Warning: Possible spoilers follow for Avengers: Endgame
Markus and McFeely specifically discuss why they didn’t include any of the Netflix Marvel heroes, such as Luke Cage, Daredevil, or Jessica Jones, in Avengers: Endgame.
“We would have to introduce these five characters — or whatever many,” McFeely explained.” We already are assuming people have seen a lot of the movies. Are we really going to assume they have bought a subscription to Netflix and watched those shows enough so that when they see them, they’re going to go “yay?'”
Source: IGN.com Why THOSE Characters Aren't in Avengers: Endgame