> Everywhere I look there is someone preserving ...

You don't know what you don't know. Just because you know of some things being preserved doesn't mean all knowledge is being preserved.

For example, the US has lost its ability to do all sorts of manufacturing.

Businesses don't tend to document internal processes publicly. As those businesses die out and the people who worked for them retire, there is no one left to pass the skills along.

That's why the Army always keeps one tank factory open. So the knowledge and skills are not lost.