Azureus has a feature where it 'queues' torrents with no other peers. When this happens, azureus doesn't announce to the tracker, so the tracker never knows that you're seeding the torrent. As a result of this, lots of torrents appear to be dead when they're really seeded by azureus users who haven't turned off the queue.
Turning this 'feature' off is vital, as you can probably tell - making torrents look dead is in no way a good thing. If you don't do this, you won't show up as a seeder on many torrents.