You are right that a lot of systems at a lot of places need 24x7. Obviously.

But there are also a not-insignificant number of important systems where nobody is on a pager, where there is no call rotation[1]. Computers are much more reliable than they were even 20 years ago. It is an Acceptable Business Choice to not have 24x7 monitoring for some subset of systems.

Until very recently[2], Citibank took their public website/user portal offline for hours a week.

1 - if a system does not have a fully staffed call rotation with escalations, it's not prepared for a real off-hours uptime challenge 2 - they may still do this, but I don't have a way to verify right now.