I have a theory, when Steve travelled back in time to return the infinity stones, he stopped for his dance with Peggy. As he knew that she had lived a happy life with a family, so if he were to intervene it would sabotage the timeline. Then I believe that once he had danced he left to return the infinity stones that were closer to the present day. Causing the avengers to be around the same age more or less, I think Cap went and married Natasha and that's why he didn't tell Sam and Bucky who he married!
This is probably a far stretch, but anything to ease the pain of Nat dying and not saying goodbye to anyone.
