further speculating, what does happen to someone sprouted/grinded? Do they get reincarnated? Do they restart their journy? Or do they really do die, making the Land of the Dead more like a second chance at life?
Plus I always thought the 9th underworld wasn't particularly a heaven or a place to strive for, but rather the enivitable resting place of souls, and the Land of the Dead was just a place where you pay off your wrongs until you experience all the pain and suffering you gave onto others. That way, when everyone truely rests in peace in the 9th underworld, they're all on equal footing, kind of leaving the world the way they came into it.
For me, I'd like to believe the difference in paying your debt verses getting sprouted/grinded is that in the latter you feel all that pain in one instant, plus your chance of living a second "life" again in the land of the dead is cut short.