Kubernetes was released in July 2015. And given that no one would have directly jumped into using Kubernetes in production in 2015, how many people do you think have 3+ years of production-level experience now in early 2020?
It may be rare, but it's not absurd. I know at least 20 people in my city alone who meet that requirement, myself included. So long as they're willing to pay a premium, it's ok to ask for exceptional levels of experience.