3½" & 5¼" Floppy Disc Drives are not the Amstrad standard yet the media and drives were far cheaper so they were common especially as a 2nd drive.
Especially the 3½" as is used because the discs are were available as used or new old stock online. You in the shops and you can also easily find such drives in any garbage if you properly scavenge old rusty computers.
Both 3½" & 5¼" drives were often double sided and supported double density and high density.
==Usage of Media==