Well Dragonbit was primarily a game store, and had more content regarding older games (primarily photos) available in South Africa more-so than OLX and Gumtree. For the US, we already have Ebay which is the biggest source we can find and even CL probably isn't needed. Goodwill and Salvation Army do not really add any value to the US list, but stores like that for other countries would be worth adding.
tl;dr: Dragonbit got to be on the list because it was more resourceful than the online classified sites, and that can be the model for getting added as a store. For US, you have to beat Ebay (good luck).