There are two reasons I have this query (spoiler alert!):
Firstly, Obito didn't have Susanoo. Considering you need to awaken both Tsukuyomi and Amaterasu, while Obito never used even one of them, how was Kakashi able to use Obito's eyes to produce Susanoo? If he copied Susanoo, then how did he do that? Is it even possible to copy something like Susanoo?
Secondly, not being of the Uchiha bloodline, he faces immense problems in using even a single eye for long periods of time. He almost lost half his chakra by making a lightning clone against Deva Path. On top of that, now he has both eyes after a long drawn battle fighting the likes of Zetsu, Obito, Madara and now Kaguya, how is he even supposed to stand?