Correct me if I am wrong, but I don't see trend that k8s is getting huge. In fact, I get a feeling that it is trying to be smaller. If you look at the release notes for each minor version, lots of in-tree features are being deprecated and users are being pointed to out-of-tree implementations. DNS, networking, metrics server, cloud vendor specific features(storage class, load balancers), container runtimes...just to name a few. And the community put great amount of effort to harden API machinery, to make it easier for 3rd parties to implement specific features for specific business.
This kind of gives me hope that one day I may be able to just run a vanilla k8s straight out of a release from github.com/kubernetes/kubernetes without any "batteries" as a platform, and I can later decide what I want to install, all by myself.