Texas has had statewide power outages. Spain and Portugal suffered near-nationwide power outages last year. Many US states are heavily reliant on the same single source for water. And remember the discussions on here about Europe's reliance on Russian gas?
Then you have the XKCD sketch about how most software products are reliant on at least one piece of open source software that is maintained by a single person as a hobby.
Nobody likes a single point of failure but often the costs associated with mitigating that are much greater than the risks of having that point of failure.
This is why "risk assessments" are a thing.