>>723644705
something that comes to mind is: the loss of institutional knowledge.
Even well-documented systems are prone to this.
another:
The necessary supporting industries (specialized machine shops and whatever else can't be done inhouse) need to be nurtured over time, or .."stimulated" I guess, by big government funding
just off the top of my head. I don't actually know the story of what major things are different between then and now, other than, I assume SpaceX designs differ than what was built in the past, or the institutional knowledge to build such things was lost