Some of these computers rely on parts that are hilariously simple individually, it's in aggregate that it becomes a computer.

For example, even a child could manufacture this with $10 worth of tools and parts:

https://en.wikipedia.org/wiki/PDP-10#/media/File:KA10_mod_en...

Keeping machines from the 00s running is going to be a hell of a lot harder than keeping machines from the 70s running