Time is an illusion, Unix time doubly so... (Jan Schaumann):

"At the time we didn't have tapes and we had a couple of file-systems running and we kept changing the origin of time," he said. "So finally we said, 'Let's pick one thing that's not going to overflow for a while.' 1970 seemed to be as good as any. "
-- Dennis Ritchie

https://www.netmeister.org/blog/epoch.html