Board Thread:Naruto Discussions/@comment-34436445-20180703141210/@comment-36351381-20180729052058

It's probably because his body and mind (without possessing Asura's chakra or the other half of Hagoromo's chakra) can't handle two rinnegan, as we see clearly in the case of Obito who isn't, or wasn't even either one of the reincarnates. Nagato accomplished this fete (possessing two Rinnegan) as a result of him being a descendant of the other half of Hagaromo's chakra (his Uzumaki-Senju lineage). Who's physical vitality could perfectly handle two Rinnegan. So in short to possess both Rinnegan you must first have both body and mind, the Uchiha are, or possess mind alone (if you understand what I mean)