Another theory

[TyrionUchiha]

BZ said that all the current White Zetsus are just people that were formerly trapped in the IT cast by Kaguya the first time. Obviously she was around long enough for her two sons to grow up and rebel against her (or else her will wouldn't manifest as the Juubi and BZ). Two things: one, when exactly did she cast IT? Did she cast it BEFORE her kids were born or after? If it was after, that leads to two: as was made apparent, only the Rinnegan can block out IT (Hinata has the Byakugan and was still captured in it, and since Hamura has Byakugan, he couldn't have blocked it out on his own), which leads me to believe that Hagoromo could use Susanoo. D:

Crazy?

 

[Seventh Sama]

Or Hagoromo broke MT with his rinnegan .-. , I think she casted IT on earth while her sons grow up on the palace on the side of the volcano.

 

[Kai NB]

Interestingly though, Hinata was the only one who was able to briefly have a conscious thought before getting caught in IT. I guess she had a very slight resistance, I'll try and find a proper image. Maybe Hamura was able to resist it better since he was one of the original users of the Byakugan?