The US has always presented itself - through media, propaganda, etc - as exemplary, greatest country in the world, home of the free / brave, leaders of innovation, technology, economics and warfare. So why not be better than the others at reducing emissions? It's a huge financial opportunity too, as exemplified by e.g. Tesla that sells cars, batteries, battery technology and solar all over the world, bringing a lot of money back to the US (in theory, assuming it's not whisked off to a tax haven like e.g. Apple and Google do).
What I'm saying here is that someone has to take the moral high ground. The US already pretends to do this, but they have the means to put it into practice.