You keep saying that the attack surface is high, but is it higher than all other software we consider suitable for this purpose?

Does anyone understand the JVM and servlet containers? Does anyone understand OpenSSL's state machine? Does anyone understand hardware load balancers? Does anyone understand speculative execution? Does anyone understand the Postgres query planner? Does anyone understand all the same-origin policies? Does anyone understand their laptop's power supply?

I've seem a lot of people build a lot of successful systems on things they don't know every detail of, even when not knowing those details is quite dangerous. That Kubernetes is yet another one of these building blocks isn't an indictment of Kubernetes, it's an indictment of the compulsion to understand everything.