Because, like Bitcoin Discussion, many good members ignore the board entirely because it is overrun with spammers. Get rid of the spammers, and they will slowly migrate back again.
You can always create self-moderated threads, moderate them however you want, and delete everything you don't want to see there without having to explain to anyone why you are doing that. The forum supports local rules, so if you have your only blacklist, you can even add rules that prevents those you consider spammers from participating in discussions. That way you will engage a better group of people in discussion or your topics will die because members will be afraid to post in them. Ignoring a whole sub-board doesn't seem like a proper solution.
How about moving any topic created from a site with "coin" in their URL and more than a few topics per month to one thread in the Press section dedicated to that site? Call it "Press releases from Coinxxxxxx.com" and it stops flooding the board with useless topics.
It's a good suggestion. If links from that site appear 5 or more times in the first 1-2 pages in the Press board, a dedicated thread just for that news site should be created. But will admins be interested in moderating it that way? We should get some feedback from them...