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.
This lasts right up until an important customer can't access your services. Executives don't care about downtime until they have it, then they suddenly care a lot.
You can often have services available for VIPs, and be down for the public.
Unless there's a misconfiguration, usually apps are always visible internally to staff, so there's an existing methodology to follow to make them visible to VIPs.
But sometimes none of that is necessary. I've seen at a 1B market cap company, a failure case where the solution was manual execution by customer success reps while the computers were down. It was slower, but not many people complained that their reports took 10 minutes to arrive after being parsed by Eye Ball Mk 1s, instead of the 1 minute of wait time they were used to.
Thousands of orgs have full stack OT/CI apps/services that must run 24/7 365 and are run fully on premise.