There are problems that people run into. One is not needing more than one computer -- if everything you need to run fits on one computer, you might as well use systemd as your orchestrator. (Which people also say is overly complicated, but really it's just extremely misunderstood.) The other is not understanding Kubernetes enough. A lot of people just explode random helm charts into their cluster and are mad that it's hard to maintain. Basically, adding another abstraction layer only helps if you can debug the actual thing on the surface -- otherwise, you're just setting a time bomb for yourself. (And, helm charts require you beg the maintainers for every feature you could possibly need, and once enough people have done that you just have raw k8s manifests where everything is called some random word instead of its actual thing. Really bad. Use Kustomize or jsonnet!)
ECS isn't exactly simple either, but it is manageable for small shops where the developer is the devops guy.
As someone who has actively avoided k8s (despite enjoying devops), my observation has been quite the opposite. At my current (small) org we have one devops guy who spends all day working on k8s related work (configuration, troubleshooting, automation, etc.) And we're about to start looking for another devops engineer because he's swamped. We only have a handful of clusters up and running so far.
k8s is the poster child for overcomplicating matters for folks that don't have Google-scale problems.