It's fair to have an opinion, and that may be why Kubernetes hasn't been rewritten in Rust, but I answered the question of why it wasn't written in Rust. It wasn't an option at the time (again, time travel is not possible).
K8s was absolutely built using exciting tech....Golang was hot off the presses. The brand new hotness. Google's internal Borg was C++, so the boring choice was C++ which wasn't chosen. Also they were google employees, which also adds a bit of bias in selection I would imagine.
