I don't think being OSS has much to do with it; it's more that the dominance of k8s leads to more people learning it, which leads to more tooling being written,

I don't think being OSS has much to do with it; it's more that the dominance of k8s leads to more people learning it, which leads to more tooling being written, which makes k8s better, which leads to more companies adopting it and more people learning it. It's a virtuous cycle much like programming languages experience.