A genuine question that I wonder about: How does a single server protect you against someone in your DC pulling a plug by mistake or your cloud provider being unreliable? If it’s a database it seems like a huge potential for going out of business.
I guess if you are running single-server databases you better have a good backup strategy anyway, but is that a risk people and businesses just accept?
If instead of using this single server (with manual fail-over in case it would fail) you'll start to create complex HA cluster from multiple servers not having enough people to properly design, test and maintain it you can end up having a less reliable system.
The tradeoffs involved in avoiding some of the simple "the cleaner unplugged the DB server" introduce complexities which may themselves cause outages which are much harder to solve.
The recent fire in a French DC saw serious disruption across all kinds of industries in many European countries. I know a sales engineer in a hardware manufacturing place, who was back to pen and paper until the IT provider figured out restores. But it wasn't that bad, as both the clients and competitors were decimated too.
That’s why you have redundant power supplies with separate power cables.