Its a common way to differentiate between kilo base 1024 (GiB) and 1000 (GB).
A GiB is 1024³MB but a GB is 1000³MB.
Windows GB are actually GiB whilst storage manufacturers disingenuously(?) use kilo base 1000 to size their products.
This is why an empty, claimed (by the manufacturer) 1TB size HDD will display as only having 931GB of free space ie. 1000,000,000,000MB in Windows.
Its never been the fashion to use GiB let alone MiB or KiB but it does have merit because it could prevent confusion. Of course users would have to understand what it meant and mostly they don't and likely don't care either.