It takes lines of supply and expertise to go into a manufacturing project. If it's so easy to just jump into an industry, why didn't the Taliban suddenly start producing a tank for every tallywacker when they knew we were on our way? A nation of restaurant owners and park administrators (that's what the liberals want America to be, a 3 million square mile park), etc. just aren't going to be able to jump back into the steel industry years after it was abandoned.
Yes. And customers. Our fair weather friends won't stop selling steel to us. Their governments waste too much money subsidising their steel industry to turn away customers with cash.