I think that has more to do with the fact the k8s devs had a complete implementation of the the same product (Google's Borg) as reference. Mesos/Marathon only had a couple 10 page journal articles to look at and a ton of on the ground decisions to make and quantify the choices of.
I’ve heard the statements that the Go stdlib and Kubernetes are not good examples of Go code, but I’ve never seen someone say that it’s not a good use case for Go. Would you mind elaborating on that assessment?