Most of them are variants on previously released sources to popular games. Dragonball Zeta, for instance, is a popular platform for these "rips". The community looks down on them because they discourage originality and generally breed ignorance. They're almost never written well and are horrible, horrible sources to learn from.

If you want to learn, I recommend these links;
http://www.byond.com/docs/guide/
http://www.byond.com/members/DreamMakers
http://www.byond.com/members/ DreamMakers?command=view_keyword_posts&keyword=tutorial
http://www.byond.com/members/ DreamMakers?command=view_favorite_resources

http://www.byond.com/members/ DreamMakers?command=view_post&post=36273 is a favorite of mine and helped me out when I was new.

It's understandable that you want to dive right in and start seeing results immediately, but if you do you're going to develop very, very bad coding habits and hurt yourself in the long run.

That being said, MasterDan's actually working on producing an opensource collection that's intended to be learned from. You can keep an eye on that here (http://www.byond.com/members/ BYONDAnime?command=view_post&post=38949).