I'm not sure where you get both "sad" and "preventable" from that documentary. The tragic decline of employment in the US steel industry was completely unavoidable.

The decline of American steel company's dominance between 1960 and 1980 might've been preventable, but the human carnage wrought by automation would've happened in any case.

Watching the documentary, you can see the coming storm. Every video of people working is a prelude to an industrial automation project. And it's no mistake that the documentary ends with an acknowledgment that today's steel workers operate a keyboard and mouse.

The most important lesson from steel is that competitive pressures + new ways of automating things = huge disruptions in the labor market (read: lots of poverty where once there was wealth).