Why does drive not enter standby mode when using hdparm -S

When reading the hdparm manual pages, it says that the -S value

is used by the drive to determine how long to wait (with no disk
activity) before turning off the spindle motor to save power

When configuring my drives with hdparm -B 1 -K 1 -S 120 /dev/sd[d-z] the output is:

 setting drive keep features to 1 (on)
 setting Advanced Power Management level to 0x01 (1)
 setting standby to 120 (10 minutes)
 APM_level    = 1

And initial drive state hdparm -C /dev/sd[d-z] is "active/idle".

All these /dev/sd[d-z] drives are off the same make and model, not partitioned, not formatted and not mounted.

After waiting for 15 minutes, the drive state is still "active/idle".

Only when issuing a "Force an IDE drive to immediately enter the low power consumption standby mode" using hdparm -y /dev/sd[d-z] the drive go to a "standby" state.

Why do my drives not enter the low power consumption standby state after the hdparm specified timeout value?

Some more drive specs derived from hdparm -I /dev/sdd

/dev/sdd:

ATA device, with non-removable media
    Model Number:       Hitachi HDS5C3020BLE630                 
    Firmware Revision:  MZ4OAAB0
    Transport:          Serial, ATA8-AST, SATA 1.0a, SATA II Extensions, SATA Rev 2.5, SATA Rev 2.6, SATA Rev 3.0; Revision: ATA8-AST T13 Project D1697 Revision 0b
Standards:
    Used: unknown (minor revision code 0x0029) 
    Supported: 8 7 6 5 
    Likely used: 8
Configuration:
    Logical     max current
    cylinders   16383   16383
    heads       16  16
    sectors/track   63  63
    --
    CHS current addressable sectors:   16514064
    LBA    user addressable sectors:  268435455
    LBA48  user addressable sectors: 3907029168
    Logical  Sector size:                   512 bytes
    Physical Sector size:                  4096 bytes
    Logical Sector-0 offset:                  0 bytes
    device size with M = 1024*1024:     1907729 MBytes
    device size with M = 1000*1000:     2000398 MBytes (2000 GB)
    cache/buffer size  = 22756 KBytes (type=DualPortCache)
    Form Factor: 3.5 inch
    Nominal Media Rotation Rate: 5700
Capabilities:
    LBA, IORDY(can be disabled)
    Queue depth: 32
    Standby timer values: spec'd by Standard, no device specific minimum
    R/W multiple sector transfer: Max = 16  Current = 16
    Advanced power management level: 1
    DMA: mdma0 mdma1 mdma2 udma0 udma1 udma2 udma3 udma4 udma5 *udma6 
         Cycle time: min=120ns recommended=120ns
    PIO: pio0 pio1 pio2 pio3 pio4 
         Cycle time: no flow control=120ns  IORDY flow control=120ns
Commands/features:
    Enabled Supported:
       *    SMART feature set
            Security Mode feature set
       *    Power Management feature set
       *    Write cache
       *    Look-ahead
       *    Host Protected Area feature set
       *    WRITE_BUFFER command
       *    READ_BUFFER command
       *    NOP cmd
       *    DOWNLOAD_MICROCODE
       *    Advanced Power Management feature set
            Power-Up In Standby feature set
       *    SET_FEATURES required to spinup after power up
            SET_MAX security extension
       *    48-bit Address feature set
       *    Device Configuration Overlay feature set
       *    Mandatory FLUSH_CACHE
       *    FLUSH_CACHE_EXT
       *    SMART error logging
       *    SMART self-test
            Media Card Pass-Through
       *    General Purpose Logging feature set
       *    WRITE_{DMA|MULTIPLE}_FUA_EXT
       *    64-bit World wide name
       *    URG for READ_STREAM[_DMA]_EXT
       *    URG for WRITE_STREAM[_DMA]_EXT
       *    WRITE_UNCORRECTABLE_EXT command
       *    {READ,WRITE}_DMA_EXT_GPL commands
       *    Segmented DOWNLOAD_MICROCODE
            unknown 119[7]
       *    Gen1 signaling speed (1.5Gb/s)
       *    Gen2 signaling speed (3.0Gb/s)
       *    Gen3 signaling speed (6.0Gb/s)
       *    Native Command Queueing (NCQ)
       *    Host-initiated interface power management
       *    Phy event counters
       *    NCQ priority information
            Non-Zero buffer offsets in DMA Setup FIS
            DMA Setup Auto-Activate optimization
            Device-initiated interface power management
            In-order data delivery
       *    Software settings preservation
       *    SMART Command Transport (SCT) feature set
       *    SCT Write Same (AC2)
       *    SCT Error Recovery Control (AC3)
       *    SCT Features Control (AC4)
       *    SCT Data Tables (AC5)
Security: 
    Master password revision code = 65534
        supported
    not enabled
    not locked
        frozen
    not expired: security count
    not supported: enhanced erase
    416min for SECURITY ERASE UNIT. 
Logical Unit WWN Device Identifier: 5000cca37dc106a3
    NAA     : 5
    IEEE OUI    : 000cca
    Unique ID   : 37dc106a3
Checksum: correct