Looks like we now know why Captain Marvel has been gone so long from earth, like 20 years, in this new "Avengers: Endgame" Clip!
We know Captain Marvel modified a 1995 beeper into an intergalactic pager and gave it to Nick Fury so he could contact her if he ever needed help. And at the end of Infinity War he did just that...before he disintegrated.
The answer seems pretty simple. It looks like she was off helping other worlds and didn't think the Avengers needed her help! In the clip she says, "There are a lot of planets in the universe and unfortunately they didn't have guys like you."
Avengers: Endgame is out April 26th...and I already have my tickets. 😉