I have a hypothesis around why people think it is complex. In my opinion it is not very complex, But the way of working, interfaces that developers deal with and formal process around k8s creates a perception that it is complex. It is also all the tools around k8s that makes it feel complex. You don't need istio, kyverno, OPA, all the other million tools from the cncf landscape to deploy your simple rails app. The industry had to paint that operating k8s hard so that they could sell tools around it. Currently version of k8s and all the stripped down versions are much easier to operate than before.

It barely takes a weekend to learn and play around with managed k8s from cloud providers or with minified k8s tools like k3s, k0s etc.