Because they're also doing more things. 20 years ago you might have a single server in the broom closet handled by the sysadmin and developers running tests loc

Because they're also doing more things. 20 years ago you might have a single server in the broom closet handled by the sysadmin and developers running tests locally (if you were lucky), nowadays we want all those things you mentioned for production, and CI/CD for developing. I'd wager providing all those things 20 years ago without k8s and CI tools would've required relatively more sysadmins