> I do not understand why organizations like Exxon-Mobil and the American Chemistry Council are promoting it.

Because if you start to look at plastics by what has to be done with them after they're consumed, they don't make sense as a common consumer product* anymore. And if they don't make sense as a common consumer product, then there's fewer people lining up to buy Exxon Mobil's plastic stocks, which are made of oil. Since Exxon Mobil is a company that exists to transfer value to shareholders via the extraction and processing of hydrocarbons, this is a problem. The ACC is made up of scientists and engineers that work for companies like Exxon Mobil.

* common consumer product meaning that it's used in places for broad public use where alternatives such as aluminum or wood are viable, like beverage cans.