Let's use a more illustrative example.
Create a table with some dummy data:
CREATE TABLE [PurchaseHistory](
INSERT INTO [PurchaseHistory]
('ZZ Top','Shampoo (Beard Wash) 16oz',3),
('ABC Stores','Fruit Punch 8oz',30),
('Nicolas Cage','Beekeeper suit',1);
If you selected this with Item/Quantity DESC, what do you expect to come out?
With the example in your question, it seems like you expect it to come out like this:
Suddenly your records now indicate that ABC stores bought 30 bottles of Beard Wash, Nicolas Cage was kind of thirsty one day, and ZZ Top is sharing a single bee suit between them.
Instead, when using ORDER BY, the values in a row are kept together, resulting in the correct data set where ABC stores is still buying 30 bottles of fruit punch, Nick Cage gets his beekeeper suit, and ZZ Top continue to have clean facial hair.