User blog comment:Looperreallyreallysucks/Pure Evil Discussion - Avengers: Endgame/@comment-25075214-20190508232420/@comment-25075214-20190509012234

Plus, the Ancient One points out that any removal of the Stones from their timelines would invoke untold chaos. Once the 2014 Thanos travelled to the present, he destroyed the time machine when he ordered his ship to attack the Avengers HQ. If he had succeeded in destroying the universe and remaking it in his own image, he would've destroyed the Stones again to ensure that his actions remain irreversible, which would put the universe in even more danger as the Ancient One feared.