The problem with having many Kubernetes clusters is that each has an operational and resource overhead. Managing one cluster is often far from trivial. Having a few is complicated. Having many can become a nightmare and requires quite a significant investment in hours dedicated to operations and maintenance.

If that overhead is not enough, we must also be aware that each cluster needs resources dedicated to Kubernetes. The more clusters we have, the more resources (CPU, memory, IO) are spent. While that can be said for big clusters as well, the fact remains that the resource overhead of having many smaller clusters is higher than having a single big one.