The Puranas have a problem that the Rigveda does not: they are trying to write a single connected account of where everything came from, and the older material gives them a crowd of gods, demons, serpents, birds and monsters with no agreed relation to one another. Kashyapa is the solution. Married to a set of daughters of Daksha, he fathers, through one wife or another, the devas, the asuras, the serpents, the birds of prey, the celestial nymphs, the cattle and a good deal else, so that the entire cast can be set out as one family tree with him at the root.
The device works because it makes the great conflict of the mythology a domestic matter. Aditi bears the gods. Diti bears the Daityas, whose name is hers. The two are co-wives in the same household, which means the standing war between devas and asuras is a quarrel between half brothers over precedence, offerings and inheritance rather than a fight between good and an alien evil. That framing is what allows the tradition to give individual asuras genuine virtue, learning and devotion without contradicting itself, and it is a very different idea from the cosmic dualism the words gods and demons suggest to an outside reader.
What Kashyapa does not have is a story of his own. He begets, he is invoked in a genealogy, and he steps aside. Almost every narrative in which he appears is about one of his children. The tradition wanted a trunk rather than a character, and it got one, which is why a figure with this much structural weight has so little attached to him: no cult, no temple, no festival, and no episode where he is the one acting.