Steve Rogers (Chris Evans) decided to stay in an alternate timeline so he could grow old with his true love, Peggy Carter (Hayley Atwell).
During an interview with the podcast Lights Camera Barstool, Joe Russo gave some insight into his and his brother’s thought process behind Steve Rogers’ timeline.
The Avengers created several branch realities in their mission to secure the Infinity Stones of the past.
Russo also confirmed that it was possible for Steve to exist in multiple realities.