Why are there so few 1" compression drivers with 1 3/8" thread?

[matthiasw]

There are not many 1" CDs with 1 3/8" thread available.
I nice exception is the BMS 5531ND for example:
https://www.bmsspeakers.com/fileadmin/bms-data/product_data_2019/bms_5531_datasheet.pdf
I am wondering why?