Argo CD, Argo Rollouts, Vault, External Secrets, Cert Manager, Envoy, Velero, plus countless operators, plus a service mesh if you need it, the list goes on. If you're providing Kubernetes as a platform at any sort of scale you're going to need most of this stuff or some alternatives. This sums up to at least multiple million LOC. Then you have Kubernetes itself, containerd, etcd...

that's not much different from using the cloud PaaS offerings besides who runs that million lines and who gets the freedom/control for customization.