8 "Unanswered Questions" From Avengers: Endgame, Explained
2. Surely There Was An Easier Way To Defeat Thanos? Like Going Back In Time To Right Before Peter Quill Messes Up Their Original Plan?
The answer to this one is the same reason Bruce and Nebula tell Rhodey he can't just go back in time and kill baby Thanos. Altering how that sequence of events went in Infinity War would splinter time, and Tony certainly wouldn't have been willing to keep living in that new timeline before the snap as he wouldn't have his family. Intervening and ensuring Quill didn't interfere would have meant there was no five years later for that timeline as it would never have had a reason to occur.
The only solution is to take the stones, bring people back after the fact of the snap, and then return the stones instantly to prevent the splintering of timelines so that nothing would have changed.