The history of that is actually a bit funny. You see, there used to be no such "fixed overhead" in early versions (including post 1.0) of k8s. This turned out

The history of that is actually a bit funny. You see, there used to be no such "fixed overhead" in early versions (including post 1.0) of k8s. This turned out to be a worse idea for less involved or experienced operators than fixed overhead, because it turned out that people would run k8s nodes way underpowered, load them with a ton of workload, then have lots of outages as they starved critical system components of resources. Because of that a (settable) "overhead minimum" was added to calculation done about available resources, iirc originally going for 0.9 cpu core and I don't recall how much memory. This allowed to still run a 2 core node (though it's really not recommended) for experimentation, while greatly lowering chances of obscure for newbies issues. It didn't prevent them (PSA: If another team provisions your cluster, check what resources they provisioned...) but it makes it much harder to fail.