WHY do Portkeys always seem to be made out of rubbish, even the ones made for use in the magical world?
If they are meant to be left where a random muggle could accidentally activate them, then it would make sense, but otherwise what is the point???
If only a magical will use them why make them inconspicuous?
Quite simply, Portkeys were required to be a piece of rubbish (or the like) so there would be the least likekihood of a Muggle stumbling into one. Dumbledore says exactly this to Harry in Half-Blood Prince:
‘You are thinking of Portkeys, Harry, which must be ordinary objects, easy to overlook.
Half-Blood Prince - page 471 - Bloomsbury - chapter 23, Horcruxes
Portkeys are highly regulated by the Ministry of Magic -- they are extremely difficult to time correctly. Think of a months-old infant crawling around and accidentally getting into a Portkey. Or the family Kneazel. But really, there aren't just Portkeys laying around, waiting to trap unsuspecting travelers. As noted (by Cornelius Fudge at the end of Order of the Phoenix) setting and maintaining Portkeys is really difficult. I doubt the Ministry would want to deal with continuous Portkey accidents.
There are, to my knowledge, three incidences of Portkeys that were created in areas that would guarantee that only magical people would use them.
Firstly, the Triwizard Cup from The Goblet of Fire, which certainly was not inconspicuous.
Next the old kettle in Dumbledore's office from The Order of the Phoenix. Though this is described as an "old kettle" and seemingly falls into the "rubbish" category, the book describes it as, "...the old kettle lying innocently on his desk." It seems that the kettle went unnoticed until Dumbledore brought their attention to it, otherwise sitting innocently on his desk. So not exactly "rubbish" but certainly inconspicuous.
Finally, the Portkey at the Ministry of Magic later in The Order of the Phoenix which was the golden wizard's head from the statue which Dumbledore had used to protect Harry from Voldemort. Certainly not "rubbish" though admittedly its value was diminished at being removed from the statue. (Additionally a wizard's head would not be very inconspicuous to Muggles.)
So in conclusion, two of the three Portkeys from canon that would be guaranteed not to be picked up by Muggles were magical in nature. So Portkey's aren't "always" made out of rubbish, and there is an indication that when the chance of a Muggle stumbling upon them is remote they can and do utilize less "inconspicuous" objects.
Note: The "guarantee" that these objects wouldn't be stumbled upon by Muggles comes from the magical protection which Hogwarts provides against Muggles stumbling onto the grounds (for the first and second example), and from the fact that the last example was created within the Ministry of Magic itself.
“What sort of objects are Portkeys?” said Harry curiously.
“Well, they can be anything,” said Mr. Weasley. “Unobtrusive
things, obviously, so Muggles don’t go picking them up and play- ing with them . . . stuff they’ll just think is litter. . . .”
Portkeys can be anything, but in world they make them trash on purpose for this exact reason.
Firstly, the Triwizard Cup from The Goblet of Fire, which certainly was not inconspicuous.– Mithical Jan 17 '16 at 09:08