You should also read further. That is not a scientific paper that is peer reviewed. It is written by someone who is not a scientist who keeps birds. We could probably easily find similarly written OPINIONS on how "habitats" are also toxic for your snake.
And you're right, we will continue to keep them in tubs - hundreds of thousands of snakes are living happy healthy lives in properly maintained tubs with perfect humidity, eating, growing, pooping and breeding in tubs all across the US. I don't recall anyone reporting an epidemic of snakes showing up with cancer as a result of doing so.