You didn't read the article. The point is that you want to use the space junk as a mass filler for your skyhook. The skyhook needs a lot of mass, a thousand times more mass than the payload. To boost a 100 ton payload, you need a 10000 ton skyhook. Junk on earth is worthless as that has to be launched into LEO.

My biggest concern however is how they are going to keep the skyhook rotating. If it needs energy from earth the entire concept is kind of meaningless.