Radio Stations do contests in an attempt to draw more listeners to the station. If it weren't for ratings you'd probably hear almost nothing in the way of contests on any radio station. Contests can be a real pain in the butt. Now there's a prize everyone will want. Some of you anyway.
Radio stations get most of the prizes they give away in contests from advertisers.
Sometimes that merchandise isn't worth a damn but the client has kicked in a little something extra for the General Manager or PD to sweeten the deal. And you get to trim the hairs in your nose. Give the poor DJ that has to give this crap away something to work with. Help him make a bit out of it. He'll love you for it.