That's because Hagoromo inherited Rikudou Chakra from Kaguya whereas Obito's only source of Rikudou Chakra came from the Juubi.
As for the topic, Obito absorbed some Rikudou Chakra from Juubidara.
Let me just point out a logical flaw in that argument.
You are saying that Hagoromo got his Rikudo Chakra from Kaguya, whereas Obito got his Rikudo Chakra from the Juubi. Now, who is the Juubi?
Okay, maybe Hagoromo has Rikudo Chakra naturally, but there's no reason not to think that Rikudo Chakra stays after loosing the Juubi.