Herein lies the problem. What happens to the environment is not governed by "humanity's best interest", it's governed by whomever has the most power and the biggest stick. These entities act in their own best interest.
To the Chinese government, more factories = more money = more power = good. To the US government, more military equipment = more power = good. At the executive level of either organization one would be laughed out of the room for suggesting environmental issues should take priority over national security.
But it's not just two countries, it's every single country making these types of decisions for 100+ years... And if $country doesn't build that weapons facility or export that labor, $otherCountry will, therefore $country will be at a disadvantage. Repeat ad infitium.
Those in power are far more concerned with maintaining and leveraging that power than they are with "humanity's best interest".