and easter eggs. Developers will implement everything that may bring money to the table. Quality of logic is dead.
try to google analog computer / analog robot this is just something simple: digitization is only one way to simplify/model the complex world. what we do is convert analog input into digital representation, process them then feeding the output back to the analog world. so by staying in the analog realm, less energy, less processing power might be required. look at the state of the A.I. now. many magic have been produced by pumping massive data into the "twilight zone". the result might be desirable / repeatable. but not many can explain how the result came to be. some have even given up with modelling. i think a critical path (aside from the nuclear) is advanced metallurgy; allowing minimal degradation of the mechanical components - ensuring stable analog responses. see also: - https://en.wikipedia.org/wiki/Sword_of_Goujian - https://en.wikipedia.org/wiki/Wootz_steel - greek fire (nothing to do with metallurgy here, but still...) they are just a small list of "lost technology". disclaimer: not a fallout fan. didn't even finish the 1st game.
in my Headcannon it always was that in the vaults they stored the elite of the elite and with all the scientists etc cuped together for years with nothing else to do resulted in an explosion of technology but with an "yesteryear" design style and after the first vaults opened the highest tech spread fast over the US of A, an the low tech died out but alas there is now a fallout 76 sigh