Paris Hilton is, or rather WAS, a celebrity just for being a celebrity.
She was famous just for being famous because she just happened to be in the news a lot. She was known for being about town, doing silly things, or buying lots of stuff.
Her apparently popularity has more to do with the inept emptiness of the media rather than any merit she possessed as a style, starlet, or even a start-up.
She was a has-been to begin with because she was a commodity, pure and simple. Since she was a fad, she would soon die away, as all fads do. Her predicament was compounded by the fact that she knew she was a fad and marketed herself exclusively on that.
Paris Hilton, we hardly knew you, nor did we care much, since we know that you were only famous for being known, and people get tired of knowing the stuff that they have already known for a long time.
Entertainment is funny like. Information is old as soon as it is released. Paris Hilton was famous for being a piece of information. Is there any surprise that she is a "has-been"?