While in construction since the late 60s, I did spend a little time in the steel fabrication industry in the early 70s. I had the privilege to work with a Dutchman that had emigrated from Holland after the war as a youngster.
Because of his wide experience he had a way of looking at things that was especially revealing. He pointed out why we had begun to buy Japanese steel. First of all, their mills were much newer than ours — thickness and related quality was superior to what came out of our older mills at that time (74). He pointed out how, like the auto industry, the steel industry had both union and management screwing over the consumer taking all they could at the trough. No concern for wages staying under foreign pressure or investment in mills that we vastly outdated. Eventually steel and cars from halfway around the world from newer plants were less costly and better quality than what came out of the rust belt.
Five years and ten years later, we began to read this same analysis in business magazines.
The bids that came in for the WTC project were so high that the project owners took a close, hard look at every line item in the cost estimate and comparing these costs to other similar projects around the world at the time. They realized that the U.S. steel was very expensive compared to the same quality materials on other projects, so they went back to the bidding contractors and told them to consider using foreign steel in their bids.
This closely coincides with the time period you described in your post.
Yep... mismanagement and greed killed the golden goose... the US had a lock on the world market post WWII but eventually these nations would and did rebuild and failing to recognize and plan for that by updating their plants and controlling costs they just bled the body from both ends union and management.