Board Thread:Boruto Discussions/@comment-1512913-20160712212432/@comment-4912646-20160714040352

Momoshiki and Kinshiki apparently harvested the chakra of the God Tree in their world for a very long time, to the point where the planet was completely drained of life. Whereas from what we see on Earth, once the chakra fruit is consumed by somebody the God Tree won't produce another until all of the chakra in the world is reunited into it. So maybe it would be impossible for both Momoshiki and Kinshiki to attain immortality by eating the fruit, since (probably) only one of them can eat it and gain its power. That's the only way it makes any sense to me.