In AWS you end up with a manually built/managed root cluster and if you've automated deploying / upgrading (which you probably should) that then you might as well just use those pipelines and code for all your other clusters too instead of having 1 special thing.

If the infrastructure gets complex there will start to be dependencies between stuff, there is definitely a tipping point where you need a real iac pipeline (tf/cf) instead in any case.

I think captn3mo proposed one of the more reasonable use cases which is provisioning stuff like queues and dbs for test envs or ci, we ended up stubbing out aws for ci and using the same pipeline code we use to deploy to prod instead for "full fat" testing but I can see where it might make sense to use kube manifests. Probably some creative uses for "deployment per customer" SaaSs too.