Distributed systems can partly fail in many subtly different ways, and you almost never notice it because there are people on-call taking care of them.

How many problems do you think there are?

I've only had one outage I could attribute to running on-prem, meanwhile it's a bit of a joke with the non-IT staff in the office that when "The Internet" (i.e. Cloudflare, Amazon) goes down with news reports etc our own services are all running fine.