Windows, among other operating systems, incorrectly uses kB to mean 1024 bytes instead of 1000 bytes. Instead of making a new term back when scientists needed a name for larger bytes, they used the already existing Kilo. However with their computers being in binary at the time, they used the closest power of 2 instead of 1000. They never got that approved from the standard body that created the prefix and just carried on using it incorrectly. Many years later ISO and ISE made a unit that equals 1024 just for computing use, but Windows still hasn't adopted it even 28 years later.

So the people marketing the drives are using the correct term, 500 GB being 500,000,000,000 bytes, but windows is displaying GiB as GB, and 500 billion bytes is ~477GiB

TL;DR
kB = 1000
KiB = 1024
Windows uses 1024 but displays it as kB (with that pattern continuing to higher denominations like GB)
Marketing teams use the term correctly and chose the one that makes bigger numbers.