You don't see how those skills would be forgotten because you're ignorant of the basics of manufacturing and have probably never worked in that industry. A working production line is kind of like a living organism: you can't just shut it down and then start it up again later expecting everything to still work. Much of the key information exists only as tacit knowledge that can't really be written down, and the actual product never exactly matches the blueprints.

There is also the supply chain to consider. Many of the parts coming from suppliers are custom or on a limited lifecycle so when orders stop the supply chain disintegrates and can't be quickly reconstituted regardless of how much money you spend.