User blog comment:B214/Question and Answers 3/@comment-25222726-20140717181240/@comment-1359322-20140718150417

It's more to the Devil inheriting only one Devil Clan ability. Either from the father or mother. Sirzechs is an exception where he inherited the Gremory and the Bael's ability. But as you can see Rias didn't. Sairaorg is almost the same case, Sairaorg gained the lion tamer instead of the POD.