That may be part of it, but not all. Still a lot of industry up there. Ohio use to have high sulfur coal, well still does, but they built scrubbing plants to remove the sulfur to reduce pollution. I grew up in Zanesville. We used to go to football games in Philo. They had a big coal fired power plant there. I remember every house was a grimy grey from the soot. Not so anymore. Cleaner coal, better filtration,...... Need a lot of money to do that. Take a look at Eastern Europe after the wall came down. An environmental disaster. It is the same in all poor countries.
It will go to a fabricator who adds more oil such as cutting, forming, drawing oils etc and it all has to be cleaned before it can be painted.
The clean water act made the rules for cleaning and treating the metal and clean air act made the rules for painting the metal.