This is just something we are trying out for now, if it doesn't work out well then it will be altered accordingly.
As Cruciform mentioned, we have to manually delete all threads. The idea was passed around of deleting them after the 30 day mark, but as Trevor and Ryan mentioned, this would involve us having to do this every day.
We haven't forgotten. A while ago Jeff set it that way on a trial basis and it just hasn't been changed back (yet).