Think of kubernetes as a cluster operating system. Instead of dealing with vms, you deal with your applications directly, without worrying about where they're running. It gives you a unified view and ability to manage a distributed system at the level of the application components.

Ansible can't give you anything like that. Even if you use Ansible to automate something like network setup, the commands and modules you use will be different between e.g. cloud providers. Kubernetes give you a consistent abstraction layer that's almost unchanged across providers, with the exception of annotations that are needed in some cases for integration with certain provider services.