GKE Persistent Disk don't get deleted when using static PV

I am testing out GKE with attaching existing disk using this GCP tutorial.
I've created a Storage Class for my storage with the reclaimPolicy set to Delete

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: pd-ssd
provisioner: pd.csi.storage.gke.io
reclaimPolicy: Delete
volumeBindingMode: WaitForFirstConsumer
allowVolumeExpansion: true
parameters:
  type: pd-ssd

However after attaching my GCP persistent disk using PV below, I found that my reclaimPolicy is set to retain again. Even after patching the PV back to Delete. The disk still fails to auto delete from my GCP Persistent Disk page (After using the disk with PVC and Pod and deleted). Am I doing anything wrong? or is this the mechanism for GCP that persistent disk can't be auto deleted when using PV static provisioning. Thank you very much for your response in advance.

apiVersion: v1
kind: PersistentVolume
metadata:
  name: test-pv
spec:
  storageClassName: "pd-ssd"
  capacity:
    storage: 50Gi
  accessModes:
    - ReadWriteOnce
  claimRef:
    namespace: default
    name: test-pvc
  csi:
    driver: pd.csi.storage.gke.io
    volumeHandle: projects/{project}/zones/{zone-of-my-disk}/disks/{my-disk-name}
    fsType: ext4

<p dir="ltr" style="line-height: 1.38; margin-top: 0pt; margin-bottom: 0pt; margin: 0;"><span style="font-size: 11pt; font-family: Arial; color: #0a0a14; background-color: #ffffff; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">As mentioned in the </span><a href="https://cloud.google.com/kubernetes-engine/docs/how-to/deleting-a-cluster#overview"><span style="font-size: 11pt; font-family: Arial; color: #1155cc; background-color: #ffffff; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: underline; -webkit-text-decoration-skip: none; text-decoration-skip-ink: none; vertical-align: baseline; white-space: pre-wrap;">document</span></a><span style="font-size: 11pt; font-family: Arial; color: #0a0a14; background-color: #ffffff; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">:</span></p>
<blockquote>
<p dir="ltr" style="line-height: 1.38; background-color: #ffffff; margin-top: 0pt; margin-bottom: 12pt; padding: 12pt 0pt 0pt 0pt; margin: 0;"><span style="font-size: 11pt; font-family: Roboto,sans-serif; color: #202124; background-color: #ffffff; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">GKE might not delete the following resources:</span></p>
<p dir="ltr" style="line-height: 1.38; background-color: #ffffff; margin-top: 9pt; margin-bottom: 0pt; margin: 0;" role="presentation"><span style="font-size: 11pt; font-family: Roboto,sans-serif; color: #202124; background-color: #ffffff; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">1. External load balancers created by the cluster.</span></p>
<p dir="ltr" style="line-height: 1.38; background-color: #ffffff; margin-top: 0pt; margin-bottom: 0pt; margin: 0;" role="presentation"><span style="font-size: 11pt; font-family: Roboto,sans-serif; color: #202124; background-color: #ffffff; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">2. Internal load balancers created by the cluster.</span></p>
<p dir="ltr" style="line-height: 1.38; background-color: #ffffff; margin-top: 0pt; margin-bottom: 0pt; margin: 0;" role="presentation">3. <a href="https://cloud.google.com/compute/docs/disks#pdspecs"><span style="font-size: 11pt; font-family: Roboto,sans-serif; color: #1155cc; background-color: #ffffff; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: underline; -webkit-text-decoration-skip: none; text-decoration-skip-ink: none; vertical-align: baseline; white-space: pre-wrap;">Persistent disk</span></a><span style="font-size: 11pt; font-family: Roboto,sans-serif; color: #202124; background-color: #ffffff; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"> volumes</span></p>
</blockquote>
<p dir="ltr" style="line-height: 1.38; background-color: #ffffff; margin-top: 0pt; margin-bottom: 0pt; padding: 0pt 0pt 12pt 0pt; margin: 0;"><span style="font-size: 11.5pt; font-family: Arial; color: #232629; background-color: #ffffff; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Persistent disks are located independently from your virtual machine (VM) instances, so you can detach or move persistent disks to keep your data even after you delete your instances.&nbsp;</span></p>
<p dir="ltr" style="line-height: 1.38; background-color: #ffffff; margin-top: 0pt; margin-bottom: 12pt; margin: 0;"><span style="font-size: 11.5pt; font-family: Arial; color: #232629; background-color: #ffffff; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">If you want to delete the disk also permanently then this can be fixed by first deleting all the namespaces. When you delete a claim, the corresponding PersistentVolume object and the provisioned Compute Engine persistent disk are also deleted.</span></p>