From the future:

AI was the stealthy nail in the coffin. We’d already experienced a century of loss of knowledge. Basic things like animal husbandry, growing crops, mining, smelting, forging…programming. all the things that used to be done by brute human strength or knowledge were now done by computers and AI. But profit was king, out with the old knowledge, in with the new lack of it.

So when the calamity finally happened, nobody was left with any of the knowledge to rebuild.