I wonder about AIs that mysteriously won't accept ceasefires.

1. It seems to me that where an AI faction is allied to another AI faction and both are at war with you, neither will accept a ceasefire even in return for land. Neither will they accept cash as a gift. They WILL though accept land as a gift and this can raise relations out of 'abysmal' which may be a step toward a ceasefire.

2. If you are excommunicated or (worse) excomm'd and also the target of a crusade, forget ceasefires. People will have no more truck with you than they will with the Muslim factions, unless they don't share a land border with you.