The reason you don't bump into k8s while selling to Hadoop users is that Hadoop isn't something you'd run on a container-based stack (at least not right now and IMO it wont be). There are lots of Hadoop users who run containers for their application infra (as opposed to data infra). Pachyderm's whole pitch is that containerized data infra can be really powerful and that enterprises will want to unify their stack to all be containerized and k8s is THE answer for the orchestration layer.
P.S. Despite all my opinions above, I actually agree with your initial question around who zetcd is actually targeting. I don't have a clear picture of that.