Ang Lee has stated that he "edits the story, not the script". Once a scene is cut, it no longer belongs to the "truth" of that cinematic world.
He has also cited respect for Heath Ledger, who died in 2008. Lee feels that releasing unreleased footage of Ledger would be a violation of the actor’s completed performance. brokeback+mountain+deleted+scenes
Everyone knows the scene in the tent. It is the pivot point of the film, the moment the dam breaks. But in the original assembly cut, there was a scene prior to that moment that the test audiences found too difficult to watch. Ang Lee has stated that he "edits the story, not the script"