I recently had a question asking why the Bloacksize property on Win32_LogicalDisk is empty but is populated on Win32_Volume.
The thing is to remember the underlying thing that these 2 CIM classes represent.
A logical disk is a subdivision of an extended partition. An extended partition can hold one or more logical disks.
When you create a volume on a disk you use either a primary partition or a logical disk from an extended partition. Until you format the volume you can’t have a block size as that is determined by the parameters you use to perform the format.
The documentation for Win32_LogicalDisk states that block size is not populated for logical disks https://msdn.microsoft.com/en-us/library/aa394173(v=vs.85).aspx.