Because no one is forcing them to. If it was in their financial interest to do better, they would. Unfortunately, the federal government has shown zero interest in protecting the Great Lakes. Obama would rather pander to business interests than protect the greatest fresh water supply in the world.
I think it goes much deeper than Obama. The more and more one looks into it, it seems that every single form of government is tainted with corporate interests. From agriculture to the protection of the Great Lakes. It seems like a complete revival of the government is the only option for change.
It certainly goes much deeper than Obama. No doubt. I happen to have a particular distaste for his Great Lakes policy with regard to the Asian carp problem. He could close the Chicago River canal into Lake Michigan by executive order this instant, but he has refused due to his cronies griping about shipping costs. The shipping costs will look like chump change when the entire Great Lakes ecosystem is ruined.