because it is intended to provide imagery about something or someone to provoke emphasis and add color. Sometimes it is used as a double
entendre - having a couched meaning.
In today's Chicago Sun-Times,
Neil Steinberg wrote about a trip he and his family took over spring break to the capitol of Illinois - Springfield. While looking for a hotel in the area to stay, he called an acquaintance at the local newspaper to inquire about lodgings. The person spoke of the main hotel in the city - the Hilton in metaphor -
"The Hilton is the most horrific piece of Freudian architecture you'll ever witness,..."
It is an apt description. Judge for yourself. Here is a photo.

Having stayed at the hotel quite a number of times in working for the state education department and attending conferences and conventions, I can, with great enthusiasm, tell you that the locals and those of us who have been to Springfield have a different metaphor for it. We refer to it as -
The Penis on the Prairieneedless to say, i prefer the
local methaphor...