If a single disk in a vSAN disk group suffers from an unrecoverable hardware failure, vSAN will mark all disks in the group with a Permanent disk loss status. This is because vSAN uses a technique called "failure domains" to ensure data availability and protect against data loss. A failure domain is a group of disks that are considered a single point of failure. If a disk in a failure domain fails, all other disks in that failure domain are also considered failed. This is to protect against further data loss in the event of a second failure in the same failure domain.
Reference:
VMware vSAN 6.7 Documentation > vSAN > vSAN Operations > Managing vSAN > Understanding and Managing Failure Domains in vSAN VMware vSAN 6.7 Documentation > vSAN > vSAN Operations > Managing vSAN > Understanding Health and Performance > Understanding Disk Group Health