It is known from the film Ant-Man and the Wasp that when anything goes into the quantum realm, it almost certainly never comes back, just as Hank Pym’s wife got lost for 30+ years. Since Professor Hulk reversed Thanos’ snap, it makes no sense to keep the Gauntlet, given the risk that Thanos will successfully or inevitably grab hold of it.
Why didn’t the Avengers throw the thing in the van, and then destroy the van? The Gauntlet would go subatomic and essentially disappear out of existence. No matter what Thanos does, he would fail to complete his goal.