Because it's better than being dead.
This. Also, there's nothing wrong with being a 'third rate realm'. Plenty of people play in one duchy or two duchy realms on Dwilight. We're not asking to appoint their ruler. We're not even demanding converts. We're simply stating that we won't permit them to retain the power to seriously threaten us again, and no peace will be possible until they have given that up or had it taken from them.
