Not only that but they are only four people of a much larger swarm maintaining the pirate bay. Even if they go to jail it wouldn't mean anything to the site being up or not.

I think this what is called being a "scape goat" - perhaps under political pressure, the courts are deciding to make an example out of them.

If jail time became the norm for running torrent sites/trackers, those who have the know how to put these things online will be more deterred than if the penalty were only financial loss.