Obito couldn't use it because the Juubi was taking over his body, he's not Ashura or Indra and therefore he can't control the 10 tails like a perfect Jin.
If you remember, Kurama was preventing Naruto from using ninjutsu when he had no control over bijuu chakra, well the same applies to Obito, the Juubi stopped him from using any form of dojutsu or ninjutsu hence why he solely relied on TSB and nothing else.
In addition Hagoromo never had the Sharingan, meaning as soon as you have his power you can't use Indra's KKG. Think of it this way, when you mix red and blue you lose both colours and get purple, same applies to Rikudou's power, when you have a Sharingan you can no longer use it the minute you have Hago's chakra.
The Sage never had Sharingan feats so having the double Rinnegan meant losing Indra's KKG in exchange for Hagoromo's. Madara was only capable of using Susanoo when he had no Rinnegan in either sockets but that changed as soon as he got his eyes back because the Rinnegan can't channel Indra's abilities.
Sasuke is the only one capable of using both dojutsu because he has the Tomoe Rinnegan which happens to be more advanced than Hagoromo's eyes and closer to Kaguya's eye from which the Sharingan originated from.