GM had a large assembly plant nearby here that made big SUVs (Chevy Trailblazer, GMC Envoy, etc) and in the mid-2000s, SUVs sales were declining and gas prices were up, so GM shut it down. It employed around 2500 people at that time. Today, SUVs are hugely popular - look at Ford's short-term plans. They're getting rid of almost all of their "cars". Are plant closures the smartest thing ? Maybe not.... For the cities or towns they are in, they can be disastrous but the folks at the top of GM, Ford, etc don't give a ***'s [censored] about that whatsoever.
I grew up in Lima OH where Ford has an engine plant. I remember when sales slowed or they had to make an engine model changeover (back then, that took months). The employees were simply "laid off" and rec'd 90% of their pay to sit at home, go on vacation, fish, etc. This is different, I realize, because these folks knew they were going back to work after a brief shutdown. Could GM decrease production with fewer working employees while the excess were laid off ? They couldn't do that for years, of course, but it might be doable. Some folks might move on and even if they did, they'd still have dibs on a job as production increased and they were needed back. Maybe it's not practical to operate with (too many) fewer employees.