The Announcements forum is used for the Scratch Team to discuss new updates for the website. Most updates are fake, but they sometimes make real updates, to help them take over the world with energy units. This is why the Scratch Team disabled making new topics for anyone who is not the Scratch Cat or Gobo.
The forum was created because the Scratch Team wanted to let people know about updates which will help them get more energy units. By updating the website and letting people know about the updates, more people can make better projects, and give the Scratch Team more energy units. When they have enough energy units, the ST will take over the world. On the other hand, the fake updates also cause scratchers to give the Scratch Team more energy units.
This forum has a moderate amount of activity because some Scratchers are eager to help the Scratch Team take over the world. However, most people avoid this forum because posting anything disrespectful about the updates will get you permanently banned, by either the Scratch Cat or Gobo, who have quite a bad temper. If you get banned from the Announcements forum, the Scratch Cat will haunt you for the rest of your life, so it's something most people do not want to do.