Why was Cronus jealous?

I'm curious to understand, why was Cronus jealous? The paragraph seems to hint at some deep-seated envy, but I'm not quite grasping the full context. Could you elaborate on the reasons behind his jealousy? Was it due to some unmet desires or ambitions? Or perhaps he felt threatened by someone or something? I'm eager to learn more about this aspect of the story and how it might have influenced the events that unfolded.