Board Thread:Theories and Speculation/@comment-25132842-20180320052324/@comment-30323490-20180320202345

^ Because Asura lacked Indra's chakra and Indra lacked Asura's chakra. Both parts replicating Hagormo's chakra.

One gained part of Hagormo's body power, and the other gained part of Hagormo's eye power. And obviously the same happened with Naruto/Sasuke and Hashirama/Madara. Naruto and Hashirama both had great life force and even became sages, and Madara and Sasuke both developed eye powerful eye powers.