Re: Before we look forwards, has it been explained why ...
In addition to the (vast) amount of existing technical documentation on those designs, there's a (probably vaster) pool of knowledge that the individuals who actually built the things collected during the process. Nearly all of those people are dead or retired now.
Most of the individual manufacturers, subcontractors, and sub-subcontractors involved have merged or collapsed, and their internal process documents may have been lost; their documentation may have been very carefully stored in a warehouse somewhere, but the guy who knows where has retired as well!
Building Apollo and Saturn required particular manufacturing processes which are now obsolete. The tools needed to make the tools to make the rockets no longer exist.
To rebuild Saturn/Apollo, we'd first have to rebuild a substantial slice of the US aerospace industry as it existed circa 1965, and all that just to be able to carry out the same kind of missions we lost interest in 40 years ago.
https://arstechnica.com/science/2013/04/how-nasa-brought-the-monstrous-f-1-moon-rocket-back-to-life/
Biting the hand that feeds IT
