The problem is that we can't just vote socialism into existence. Even if Sanders were elected president–and the bipartisan U.S. political system has and will continue to deploy every trick to make sure he's not–most of the wealth by far that could be redistributed is the private property of the 1 Percent.
That's the biggest reason we can't seem to stop climate change: the laws of capitalism say we can't stop oil companies from pumping out their oil, even if it destroys our species.