The server doesn't know where the physics bricks are. The server has to know where stuff is for you to be able to stand on it. Otherwise the server has to take your word for it, which means that there will be a lot of cheating as people tell the server they are flying through the air/going through walls.
If everyone had really fast connections and really fast computers we could do something about that, but they don't. Maybe in a few years.
Trust me, it's plenty fun as it is, and you will have a great time shooting explosives at things. The fake-killed bricks move naturally when you or a vehicle or an explosion shove them around after they have been exploded.