Despite his heroic nature, one could say that Steve Rogers is a control freak more than Tony Stark is and given Steve more heroic holy than thou attitue, you could get a bit annoyed with him.
So I can see why Sam would split from him given his actions in Time Runs Out, that is if the heroes recall the events of Time Runs out Post Secret Wars, and if not that, then it has to be due to his sometimes controlling nature of the given situation.
However, what do you all think of the split between Steve and Sam post Secret Wars and what do you think caused that ?