When it comes right down to it, a breeding thread is a trading thread. People still have to offer something for the bred pokemon, so most wouldn't consider threads like that any different from normal threads, so the need for a sub-forum is not very strong, IMO. Seems like too much organization =/
Not to mention, there's so much activity in the trade center that you almost have to check the second page to see all the new posts. I've seen plenty of thread bumped from the third or fourth page, so people know to look beyond the most recent posts. The trade corner is a busy place, and we just have to live with it.