Because the English Language Is Colorfully Bland ...
oxymoron [oksi‐mor‐on] (plural ‐mora), a figure of speech that combines two usually contradictory terms in a compressed paradox, as in the word bittersweet or the phrase living death.
Here are a few favorites ... what are yours?
"Jumbo shrimp" (thx, VB)
"White Chocolate" (thx DL)
"Government intelligence" (thx GWB, and many, many others, too numerous to list!)
"Microsoft Works" (thx BG)