You wouldn't believe the amount of critical infrastructure that's running on 60's tech that barely anyone still alive knows how to maintain let alone build again. This stuff is ancient but its reliable, almost bulletproof, and it was a huge investment which means it would take a similar if not bigger investment to replace with a more modern but unproven version so its left alone, "not broken, don't fix it".
One particular case I know is of a major industrial facility (wont powerlevel) that needed to fix systems that were written in FORTRAN which is even older than COBOL. The only guy still alive who had the knowledge to fix that had been retired for nearly 30 years, they sent company reps to find him camping near a lake only for him to tell them "I'm done with that", I shit you not its like something out of an action movie when they go looking for the hero except the guy was a literal pocket protector-wearing square glasses nerd from the space age.