Board Thread:Naruto Discussions/@comment-34569788-20180504183427/@comment-734582-20180506135837

LegionZero wrote: Total speculation. There is nothing to suggest that Hagoromo did anything other than grant those abilities unto the 2 of them. It is questionable whether or not Tailed Beast chakra is necissary for 6 Paths Sage Mode. Naruto's SPSM is unlike normal six paths senjutsu, while Sasuke's Rinnegan is unlike other rinnegan. I think it's fairly obvious that Hagoromo is the reason why they are different. The fact that he could take something and change it as he saw fit as he did with the Juubi, proves that it's well within his power.

Sasuke got hashirama cells, but it can take decades to awaken Rinnegan. Sasuke got it instantly. Naruto had the Biju's chakra, yet did nothing and couldn't use it until Hagoromo came along. Clearly, hagoromo did something with the Biju. We don't know what, but it resulted in Naruto's SPSM.

From multiple angles, it all comes back to the fact that Hagoromo somehow intervened with their power, giving Sasuke his unusual eye and Naruto his unusual Sage Mode.