Patents and service manuals are not designs. They are just symbolic representations to illustrate the principles of operation. For manufacturing you need exact dimensions and tolerances for every part.

And the tolerance stackup is what makes it both expensive and reliable.

A whole lot of people are going to get a simple introduction into why some things are expensive.

Exactly. This is like handing someone a published API and asking why they can't just compile and run it.

Patents and service manuals are most of what you need to start reinventing the wheel. They're what you hand your R&D staff as you start reverse-engineering something, learning along the way all the little tricks that make it harder than it looks. They're not what you hand your machine shop and start producing.