Non-containerized environments (VMs, bare metal) are well-understood and fairly predictable; Docker and Kubernetes are moving targets. There are "known unknowns".
As an example, I am involved in a project that uses continuous delivery for deploys, and we recently had an incident where the GKE node ran out of inodes because Docker was keeping all the layers of dead containers around. Kubernetes handles this correctly: Best-effort pods were evicted and the node went back to being ready once the inode use went down. PostgreSQL would have stayed up in this case, but it was still a little surprising that GKE, which is nominally managed, does not have a process in place for cleaning up Docker's garbage. (Edit: Apparently it's a bug [1].)
When discussing Docker and Kubernetes, there are very often edge cases that come up. For example, until a couple of months ago, Kubernetes had a serious bug that would often cause the wrong network volume to be mounted to a new pod. You can be the world's best containerized-database admin and still be surprised by things like this, which have nothing to do with the nature of containers, and everything to do with the specifics of the software that controls them.