Not all bottlenecks scale linearly (and "bottleneck" was just one of several words I used). I'm sure Kubernetes is well-designed and battle-tested, but to most developers these are black boxes that need to be studied and learned, each with its own set of complexities and workarounds and warts. And so on.
Moving parts are moving parts no matter how well they are designed. More of them always add complexity, by definition; they never reduce it.
It does win on setup for sure. This isn't an easy problem to solve however.