Kubernetes was originally intended to act as a container orchestration platform for stateless workloads, not stateful apps. StatefulSets run the gamut from databases, queues, and object store to janky old web applications that need to modify a local filesystem for whatever reason. The StatefulSet controller has no built-in support for volume resizing. This is despite the fact that almost all CSI implementations have native support for resizing the controller could hook into. There is a workaround, but it’s almost ludicrously roundabout.