The U.S. government has been comparatively strict regarding emissions from painting systems. This has caused the U.S. auto companies to change the way they paint. The Big Three couldn't. As you go from high-solvent to low solvent your operating window closes down. But regulations mean that companies painting in the U.S. can't do it.
Emissions are the concern.
In the parlance of automotive paint, emissions aren't just considered to be the fumes that want to make their way into the atmosphere. What's more, the abatement equipment consumes energy and produces, as a byproduct, NOx, which isn't prohibited, but which isn't ideal, either. Emissions are also what get sprayed in the paint booth but don't make it onto the object being painted. What happens is that the overspray falls to the floor of the paint booth, which is a grating over water. But there is an issue that has to be addressed in a comprehensive way in order to bring this promise to fulfillment.