Strange was also right there, and he let it happen. Which leads me to believe that in at least SOME of the futures he saw, they DID get the Gauntlet off of Thanos, one of them tried to use it, and all kinds of hell broke loose by accident. It was made specifically for Thanos alone, remember.
Because, horrible and stupid that he is, Thanos DID have a goal and the will to toss nigh-omnipotence away upon achieving that specific goal. Someone without that willpower (any of the Guardians), or with terrible self-doubts (Stark), or immaturity (Spider-Man), and no concrete idea of HOW to use the Gauntlet could cause irreparable harm to the universe.
"A person is smart. People are dumb, panicky, dangerous animals and you know it. Fifteen hundred years ago everybody knew the Earth was the center of the universe. Five hundred years ago, everybody knew the Earth was flat, and fifteen minutes ago, you knew that humans were alone on this planet. Imagine what you'll know...tomorrow."