Why did old PCs have key locks?

Great Video! Minor nitpick (And he did mention that he wasn't counting things like workstations and servers), but the history of Key locks on desktop size computers was not a novel idea in 1984.

At my university there's a busted Data General Nova (1969) front panel with the lock cut out gathering dust in a cardboard box. I wouldn't be surprised if even earlier computers had locks, although most probably weren't desktop size like the Nova.